Patent Application
20190184515
The present invention relates generally to a machine for processing workpieces in optical quality according to the preamble portion of claim 1. In particular, the invention relates to a machine for grinding and/or polishing such as used in, for example, the precision optical industry on a large scale in lens, mirror and mold production.
The processing of workpieces in optical quality by material removal can be roughly divided into two processing phases, namely initially the preliminary processing of the optically effective surface for generation of the desired macrogeometry (or topography) and then precision processing of the optically effective surface in order to eliminate preliminary processing tracks and obtain the desired microgeometry. Whereas preliminary processing of the optically effective surfaces for imparting shape is carried out, inter alia, in dependence on the material of the workpieces by grinding (for example in the case of lenses of mineral glass), milling (for example in the case of metallic mold inserts) and/or turning (for example in the case of plastics material lenses), the optically effective surfaces of workpieces in precision processing for achieving the desired surface roughness are usually subject to a precision-grinding, lapping and/or polishing process. Insofar as the term “processing”, also in word combinations such as, for example, “processing tool” or the like, is used in the terminology of the present application this shall embrace material-removing preliminary and precision processing, primarily with a geometrically undefined cutter and incorporated grain (grinding) or loose grain (polishing).
Currently, one machine or in a given case several machines with a large number of precisely running tools is or are required for carrying out more complex processing sequences. Since the change from one machine to a downstream machine requires time and, due in part to different clamping systems for workpiece mounting, also involves the risk of rechucking errors, machines equipped with several processing spindles have already been proposed in the prior art.
Thus, document DE 19750428 Al discloses a device for polishing optical lenses on both sides, in which a pivot head is present at a machine frame in the upper part, which pivot head is pivotable about a pivot axis and carries a tool spindle for an upper shaping tool for processing a convex lens surface as well as a “multi-purpose spindle” for an upper “multi-purpose tool”, which comprises an inner dressing tool and an outer tool mount. Arranged in the lower part of the machine frame is a horizontally movable X slide connected with a vertically movable Z slide, which in turn carries a further tool spindle for a lower shaping tool for processing a concave lens surface as well as a further “multi-purpose spindle” for a lower “multi-purpose tool”. The latter similarly has an inwardly disposed dressing tool and an outwardly disposed tool mount.
With this device (a) the two shaping tools can be dressed with the respectively opposite dressing tool of the corresponding “multi-purpose tool”, (b) a lens initially held in the workpiece mount of the lower “multi-purpose tool” can be processed at its convex lens surface by the upper shaping tool, (c) the lenses can be transferred from the workpiece mount of the lower “multi-purpose tool” to the workpiece mount of the upper “multi-purpose tool” and, finally, (d) the lenses then held in the workpiece mount of the upper “multi-purpose tool” can be processed by the lower shaping tool at the concave lens surface thereof. However, a disadvantage of this device is to be seen in the fact that particularly as a consequence of the physical proximity of the spindles of the respective spindle pair at the pivot head or at the Z slide and the length of the spindles mounted on the pivot head it is significantly limited not only with respect to the processible workpiece geometries, but also with respect to the size of the workpieces to be processed.
A grinding and polishing machine which is significantly more flexible by comparison with this prior art, for grinding and/or polishing workpieces in optical quality, is known from document DE 10 2006 028 164 A1, which defines the preamble portion of claim 1. This machine comprises, in a very compact mode of construction, two workpiece spindles, by way of each of which a respective workpiece to be processed can be driven to rotate about a workpiece axis of rotation, and a pivot head which is opposite the workpiece spindles and pivotable about a pivot axis. The pivot head carries two parallely arranged tool spindles, each of which is constructed at the two ends for coaxial mounting of a respective processing tool and can be driven for rotation about a respective tool axis of rotation extending transversely to the pivot axis. The workpiece spindles and the pivot head are, in addition, adjustable relative to one another along three mutually perpendicular linear axes, of which one linear axis (Y) extends parallel to the pivot axis, whereas another linear axis (Z) extends parallel to the workpiece axes of rotation.
In this prior art it is possible in advantageous manner for the tool spindles to be rotated by way of the pivot head with respect to the workpiece spindles not only statically, but also dynamically in any defined angular positions between 0° and 360°, in which case, for example, a tool change can be carried out by pivotation of the pivot head through approximately 180° about the pivot axis so that a downstream processing step is made possible at one and the same workpiece surface. Moreover, due to the linear axis (Y), which is additional by comparison with the prior art outlined in the introduction and which extends parallel to the pivot axis, further workpiece geometries can be processed, which is of advantage particularly in view of the circumstance that in the precision optical industry a stronger trend towards more complex components, in particular with aspherical surfaces and free-shape surfaces, can be observed.
However, the processing possibilities in the prior art defining the category reach their limits when very large workpieces or workpieces with large changes in topography have to be processed. Due to the constructional form of the tool spindles and the necessity of a stiff spindle mounting there arise at the pivot head, in particular, disruptive contours which in the past have prevented processing of such workpieces, otherwise there is the risk of damage of machine and/or workpiece as a consequence of unintended collisions between spindle housing and workpiece.
The invention has the object of creating a machine, which is constructed as compactly as possible, for processing workpieces in optical quality, which machine is usable as universally as possible and thus allows different processing strategies, especially even the processing of large workpieces or workpieces with large changes in topography and with a high level of accuracy.
This object is fulfilled by the features indicated in claim 1. Advantageous or expedient developments of the invention are the subject matter of claims 2 to 15.
According to the invention, in a machine for processing workpieces in optical quality—which machine has at least one workpiece spindle, by way of which a workpiece to be processed is drivable for rotation about an axis C of workpiece rotation, and a pivot head which is opposite the workpiece spindle and which is pivotable about a pivot axis B and carries at least two tool spindles, at each of which at least one processing tool is held to be drivable for rotation about an axis D, D′ of tool rotation, wherein the workpiece spindle and the pivot head are in addition adjustable relative to one another along three mutually perpendicular linear axes X, Y, Z, of which one linear axis Y extends parallel to the pivot axis B, whereas another linear axis Z extends parallel to the workpiece rotational axis C—at least one tool spindle is mounted on the pivot head with its tool rotational axis D′ extending parallel to the pivot axis B.
Through the rotationally parallel arrangement of tool spindle and pivot head it is possible to displace an engagement region at the circumference of the processing tool held at this tool spindle, by which the processing tool can be brought into processing engagement with a workpiece which is held at the workpiece spindle and is to be processed, referred to the pivot axis B of the pivot head and the other tool spindle at the pivot head in a processing plane, which is aligned with the third linear axis X, radially outwardly transversely to the pivot axis B, facing away from the other tool spindle. In this way, a very compact pivot head and tool spindle combination results which makes possible a “circular locus” of the processing tools of maximum size without an individual large three-dimensional extent during the processing. As a consequence thereof, even very large workpieces or workpieces with large changes in topography and/or pronounced inclinations can be processed without problems with lengthy travel paths along the linear axis X and/or large pivot angles about the pivot axis B, without the risk of collisions between the pivot head or the tool spindles mounted thereon and the workpiece.
Both grinding tools and polishing tools can be used as processing tools at the tool spindle arranged parallel with respect to the pivot axis B. These tools can be spherical or also have only an engagement region, which has the shape of the segment of a sphere or a section of a sphere, with respect to the workpiece, or can be discoid. In the case of use of, for example, a circumferential grinding wheel a separate edge processing is possible, so that in downstream processing procedures the workpieces can be oriented more easily and precisely, which is important particularly for measurement tasks. With the assistance of this tool spindle and suitable processing tools it is also possible for facets to be machined at the workpieces and, in particular, not only at round workpieces, but also at workpieces with any edge geometry, since the risk of unintended collision with other processing tools or spindle components is minimized.
In summary, the concept according to the invention makes it possible, with low constructional outlay, to bring the most diverse processing tools into engagement, with precise running, with the respective workpiece to be processed, so that a large number of more complex surfaces and components can be processed largely with avoidance of special tools. In particular, all common grinding and polishing methods can be carried out, including rotary circumferential transverse and length processing, external cylindrical grinding and polishing, cup grinding and face grinding and polishing. In the case of use of particularly narrow grinding wheels there is in addition a possibility of sawing or separating so that, for example, prisms can also be produced.
For preference, the arrangement of tool spindles at the pivot head is such that the engagement region of at least one of the processing tools mounted thereon, which can brought into processing engagement with the workpiece, defines a radially outer circular locus of the pivot head about the pivot axis B, i.e. a circular locus beyond which no other processing tool or spindle part projects. Thus, it is advantageously possible to rapidly change from this processing tool, through a pure pivot movement of the pivot head about the pivot axis B, to a different processing tool without a linear travel plan or linear deflection movements being necessary for that purpose.
In further pursuance of the concept of the invention the engagement regions of all processing tools can have substantially the same radial spacing from the pivot axis B. Thus, through pivotation of the pivot head about the pivot axis B a change between any processing tools at the pivot head is possible; larger linear movements are not needed for that purpose, as a result of which processing downtimes are minimized.
Moreover, the arrangement can be such that the engagement regions of the processing tools are substantially uniformly angularly spaced from one another with respect to the pivot axis B. This advantageously ensures a minimum of disruptive contours at the pivot head. The individual processing tools can be pivoted to an equal extent about the pivot axis B, which in turn is of advantage with respect to the processing of large workpieces and/or surfaces with large differences in height.
Moreover, for preference at least one (further) tool spindle is mounted on the pivot head with its tool rotational axis D extending transversely to the pivot axis B, whereby the use of, for example, cup tools is possible. This is conducive to a largest possible multiplicity of processing procedures and strategies. In that regard, the tool spindle can in principle be constructed at merely one end for mounting a processing tool. However, by contrast a design is preferred in which the tool spindle with the tool rotational axis D extending transversely to the pivot axis B is constructed at both ends for coaxial mounting of a respective processing tool. Thus, two processing tools can be driven in more space-saving and economic manner by only drive. If, for example, a spherical or discoid grinding tool is used at the tool spindle with the tool rotational axis D′ extending parallel to the pivot axis B, whereas the tool spindle with the tool rotational axis D extending transversely to the pivot axis is equipped at both ends with cup tools, several successive processing steps are advantageously possible in one workpiece chucking. Thus, for example, preliminary grinding by the first cup tool, precision grinding by the second cup tool and finally ultra-precision processing by the spherical or discoid tool rotating parallel to the pivot axis B, whereby overall a high level of surface trueness and at the same time an increase in individual tool service lives and thus also a higher level of machine serviceability and productivity are the result.
For preference, a center of mass of the pivot head carrying the tool spindles lies on or at least close to the pivot axis B, thus in the immediate vicinity thereof. This has the advantage that for pivotation of the pivot head about the pivot axis B only a small amount of drive power is needed. In addition, eccentricities at the pivot head which can be detrimental to high processing accuracy are avoided. Processing procedures which during engagement of the processing tool with the workpiece require pivotation of the pivot head about the pivot axis B can advantageously be executed in highly dynamic manner.
For rotary drive of the tool spindle with the tool rotational axis D′ extending parallel to the pivot axis B various drive concepts of short construction are possible, for example a chain drive or a drive by way of a gearwheel transmission. However, in order achieve high rotational speeds with low wear and substantial running quietness it is preferred if for rotational drive of the tool spindle with the tool rotational axis D′ extending parallel to the pivot axis B there is provided a belt drive with a spindle motor which is arranged parallel to the spindle shaft and which is in drive connection with the spindle shaft by way of a belt.
In principle, it is conceivable to provide in this case a tensioning roller between the spindle motor and spindle shaft for tensioning the belt. However, with respect to a lowest possible outlay and a very compact form of construction it is preferred if the spindle motor is mounted to be pivotable relative to the spindle shaft for tensioning the belt.
For preference the belt of such a belt drive is a poly-V-belt. Belts of that kind offer a high level of force transmission in little space with a highest degree of stability as well as running quietness and this even in the case of high drive speeds.
In principle, a ball spindle drive or the like can be used for adjustment of the workpiece spindle along the linear axis Z. However, it is preferred to mount the workpiece spindle for adjustment along the linear axis Z on a Z slide which is guided by way of a guide arrangement at a machine bed and which is movable by means of a linear motor relative to the machine bed. The use of a linear motor for axial movement of the workpiece spindle is not only advantageous to the extent that readjustment without a reversing spindle can be carried out more dynamically and accurately, but particularly also because a power-regulated grinding process can be carried out such as described in document DE 10 2012 010 004 A1. For such a process, in which the linear motor predetermines a variable feed power by way of the motor current, instantaneous power relationships are inferred on the basis of target and actual directions of feed movement and as a result thereof the feed power is influenced by way of motor current in process-dependent manner, the material removal performance during grinding, in particular, is optimized. The result is in advantageous manner significant reductions in processing times, elimination of safety spacings, simple initial cut recognition and more reliable prevention of overload states of workpiece and tool due to high feed speeds or due to collisions.
Moreover, the guide arrangement for the Z slide can be equipped with clamping elements by way of which the Z slide is fixable relative to the machine bed. It is possible through measures of that kind to avoid undesired sinking of the Z slide in the case of emergency shutdown or servo-off (shutdown of drives) of the machine. Moreover, the linear axis Z can be established more favorably in terms of energy for specific processing procedures such as, for example, separating processes, also in order to increase the stiffness during processing.
For preference, the machine is additionally provided with a device for weight compensation for the Z slide carrying the workpiece spindle. As a result, processing procedures can advantageously be operated in a particularly highly dynamic manner without the risk of “overshooting”, which is caused by gravitational force, in the movement along the linear axis Z. In principle, it is conceivable to use, as device for weight compensation, a counterweight which by way of a deflecting and braking mechanism supports the Z slide with the workpiece spindle mounted thereon. However, with respect to a compact design, rapid reaction times and good controllability it is preferred if the device for weight compensation comprises at least one pneumatic cylinder which is arranged between the Z slide and the machine bed and can be acted on pneumatically in order to counter the weight of the Z slide carrying the workpiece spindle. This makes possible a highly sensitive setting of the position of the Z slide by means of the linear motor and additionally assists the above-discussed power-regulated grinding process with the help of the linear motor.
Finally, in a further, preferred development step the pivot head can be provided with a functional element for detecting the workpiece geometry. In that regard it can be, for example, a scanner or a ring spherometer according to DIN 58724, which is mounted laterally at the outside on the pivot head or one of the housing of the tool spindles. In this way it is possible, without additional movement axes, to carry out measurements of the workpiece geometry directly before, during or after different grinding steps in situ and automatically take into consideration possibly required corrections by the CNC control. It is possible through the pivotability, which is given by way of the pivot head, of the scanner or the spherometer about the pivot axis B to place the respective functional element aligned to normal on any desired point of the workpiece, whereby—not least—erroneous measurements due to oblique scanning are avoided.
The invention is explained in more detail in the following on the basis of preferred embodiments with reference to the accompanying partly simplified or schematic drawings, which are not true to scale, wherein the same or corresponding parts are provided with the same reference numerals. In the drawings:
The machine 10 comprises a machine bed 20, which is formed from a monolithic block of a mineral casting (“polymer concrete”). Two guide rails 22 extending parallel to one another in the horizontal width direction x are secured to the machine bed 20 on the upper side of the machine 10. The two guide rails 22 are bounded by end abutments 24. An X slide 26 is guided by way of guide carriages 28 on guide rails 22 to be displaceable and is adjustable under CNC positional regulation in both directions of the linear axis X by a linear motor 30. The current-conducting primary part 32 of the linear motor 30 is attached under the X slide 26, whereas the passive secondary part 34 is arranged between the guide rails 22 at the machine bed 20.
Two guide rails 36 extending parallel to one another in the horizontal length direction y are attached to the X slide 26, as can be best seen in
The Y slide 38 carries a pivot drive 48 for the pivot head 14, by means of which the pivot head 14 is pivotable about the pivot axis B under CNC rotational angle regulation, thus with a defined angular position. It will be apparent that the slides 26, 38 thus form an X/Y cross-table arrangement, by means of which the pivot head 14 is adjustable in a horizontal plane in which the pivot axis B lies. The tool spindles 16, 18 are mounted at the pivot head 14 in an arrangement adjacent to one another so that the tool spindle 16 extends by its tool rotation axis D transversely to the pivot axis B, whereas the tool rotational axis D′ of the tool spindle 18 extends along the pivot axis B. The arrangement is in that case such that a center of mass of the pivot head 14 carrying the tool spindles 16, 18 lies on or at least close to the pivot axis B.
Further details with respect to the pivot drive 48 can be inferred from
Further details of the tool spindle 16 can be inferred from
Details with respect to the second tool spindle 18 mounted on the pivot head 14 near the afore-described first tool spindle 16 can be inferred from
As can be inferred from, in particular,
According to
Finally, a sensor arrangement which, for sensing the rotational speed of the spindle shaft 88 is fastened to the base 78, is indicated in
As can be further inferred from
According to, in particular,
As further apparent from
In addition, the machine 10 is equipped with a device 140 for weight compensation for the Z slide 124 carrying the workpiece spindle 12. In the illustrated embodiment, the device 140 for weight compensation comprises two pneumatic cylinders 142 which are arranged in parallel in the Z slide 124 and which are disposed between the Z slide 124 and the machine bed 20 to be effective in terms of actuation and can be acted on pneumatically to counter the weight of the Z slide 124 carrying the workpiece spindle 12. More precisely, the pneumatic cylinders 142 according to
Finally, the workpiece spindle 12 is received and fastened in suitable manner in an associated cut-out 152 (see
According to
In the embodiment illustrated here, even the engagement regions E1, E2, E3 of all processing tools T1, T2, T3 have substantially the same radial spacing from the pivot axis B. Moreover, the engagement regions E1, E2, E3 of the processing tools T1, T2, T3 are substantially uniformly angularly spaced from one another with respect to the pivot axis B, namely by approximately 120°.
When this processing step, which can serve for, for example, preliminary processing of the lens L, has ended, the pivot head 14 can be pivoted, for example for the purpose of precision processing of the lens L, until the cup wheel T2 held at the other end of the tool spindle 16 is opposite the workpiece spindle 12 (not shown), whereupon in analogous manner the rotating lens L is processed by means of the similarly rotating cup wheel T2 (fixed pivot angle about the pivot axis B, adjustment along the linear axis Z and feed along the linear axis X).
An ultra-precision processing step carried out by the circumferential grinding wheel T3, which is mounted on the tool spindle 18 oriented in parallel to the pivot axis B, corresponding with the respective processing requirements can then follow that. This is illustrated in
It will be apparent that no tool change and also no tool re-adjustment are needed for the afore-described processing sequence, since the required tools T1, T2 and T3 are already all present at the pivot head 14.
In
In the processing example of
Finally,
A machine for processing workpieces in optical quality comprises at least one workpiece spindle, by way of which a workpiece to be processed is drivable for rotation about an workpiece rotational axis C, and additionally has a pivot head, which is opposite the workpiece spindle and which is pivotable about a pivot axis B and carries at least two tool spindles, at each of which at least one processing tool is held to be drivable for rotation about a tool rotational axis D, D′. In addition, the workpiece spindle and the pivot head are adjustable relative to one another along three mutually perpendicular linear axes X, Y, Z, of which one linear axis Y extends parallel to the pivot axis B and another linear axis Z extends parallel to the workpiece rotational axis C. At least one tool spindle is mounted at the pivot head with its tool rotational axis D′ extending parallel to the pivot axis B, which allows a multiplicity of different processing strategies, particularly also the processing of large workpieces and workpieces with large changes in topography with a high level of accuracy.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 006 791.8 | Jun 2016 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/000660 | 6/7/2017 | WO | 00 |
