Centering machine for workpieces, particularly optical lenses with curved optical surfaces

Description

TECHNICAL FIELD

[0001] The present invention generally relates to a centering machine for workpieces used in the precision optics, watchmaking, and semiconductor industries, where workpieces are first clamped in a centered manner and subsequently machined and / or scanned at the edges. Specifically, the invention relates to a centering machine for optical lenses with curved optical surfaces, in which a lens is clamped in a centered manner for its edge machining using the so-called "bell clamping method" or "process." STATE OF THE ART

[0002] Lenses for objectives or similar devices are "centered" after the optical surfaces have been machined so that the optical axis, whose position is defined by a straight line passing through the two centers of curvature of the optical surfaces, also passes through the geometric center of the lens. For this purpose, the lens is first aligned and clamped between two aligned centering spindles so that the two centers of curvature of the lens coincide with the common axis of rotation of the centering spindles. The edge of the lens is then machined in a defined relationship to the optical axis of the lens, as is later necessary for the lens to be mounted in a mount.Depending on the material of the lens (glass or plastic), the edge is given a defined geometry by machining with geometrically undefined or defined cutting edges, both in the top view of the lens - circumferential contour of the lens - and in the radial section - contour of the edge, for example a straight line or a step(s) / facet(s).

[0003] The "bell clamping process" mentioned above refers in this context to an alignment and clamping process in which the lens is automatically aligned with its optical axis between the cup-shaped clamping bells provided on the centering spindles, for example, relative to the vertically running rotation axis of the centering spindles, before it is clamped. For this purpose, if the centering spindles are arranged vertically, for example, the lens is placed on the clamping bell of the lower centering spindle, whereupon the clamping bell of the upper centering spindle is moved axially relative to the lower clamping bell - either by lowering the upper centering spindle or raising the lower centering spindle - until the upper clamping bell also rests against the lens with slight pressure (contact phase). The lens now shifts due to the curvature of its optical surfaces, if necessary.With the addition of a suitable lubricant and / or rotation of the centering spindles, the lens is automatically moved in the transverse direction, with the clamping bells moving further together (alignment phase). The transverse movement of the lens relative to the clamping bells, as well as the axial relative movement of the clamping bells, ends when the lens has assumed a position between the clamping bells that allows the minimum distance between the clamping bells under the given geometric conditions. The lens, now aligned with its optical axis relative to the rotational axis of the centering spindles, is now clamped firmly between the clamping bells by increasing the clamping force (clamping phase) and can then be machined at the edge. While the clamping or centering bells - sometimes also referred to as "clamping or centering mandrels" - are standardized for optics production (the German standard DIN 58736-3 from July 2001 is expressly referred to in this regard), centering machines adapted for this process, e.g.known from the documents DE-A-37 44 118 (corresponding to the document EP-A-0 323 572) and DE-A-100 08 710.

[0004] The centering machine disclosed in the closest publication DE-A-37 44 118 has two centering spindles arranged one above the other. The centering spindle shafts, which can be driven in rotation via belt drives acting on one side, are axially aligned with respect to a centering axis and are designed to receive a clamping bell at their facing ends. In this prior art, the upper centering spindle is designed as an axially fixed spindle (fixed spindle), while the lower centering spindle is axially movable and clampable with respect to the upper centering spindle (clamping spindle).To generate these axial movements and forces, a pressure medium device is provided. This device has a plate-shaped yoke arranged below the clamping spindle. In this yoke, a diaphragm piston-cylinder unit is arranged centrally to the clamping spindle. This unit acts on the lower end of the clamping spindle. On either side of the centering axis, a double-acting pressure cylinder with a short-stroke and a long-stroke piston is attached to it. While the pressure cylinders, with simultaneous pressure on the short-stroke and long-stroke pistons until the long-stroke pistons contact the short-stroke piston, generate the stroke required to move the clamping bells together to a small gap between the upper clamping bell and the lens resting on the lower clamping bell, the diaphragm piston-cylinder unit serves as a (fine) lifting device for the lens alignment process, by means of which the force required to align the lens can be adjusted.The clamping force required to machine the lens, which exceeds the force generated by the diaphragm piston to align the lens by several times, is then generated solely by the long-stroke pistons after the pressure acting on the short-stroke pistons has been switched off, with the diaphragm piston resting on the yoke so that the clamping force of the long-stroke pistons acts fully on the clamping spindle.

[0005] However, this state of the art requires improvement in several respects to ensure the most optimal bell clamping process possible: For example, the proposed parallel arrangement of the double-acting pressure cylinders, in addition to the relatively high internal friction, poses the risk of "tilting" of the long-stroke pistons, also due to the stick-slip effects that vary from piston to piston. Furthermore, the diaphragm piston has a certain inherent rigidity, which is why the force required to align the lens cannot be adjusted very precisely. Furthermore, especially if the centering spindle shafts are driven in rotation during the bell clamping process, a transverse force is introduced at the centering spindles, which can cause a certain degree of bending and / or transverse displacement of the centering spindle shafts in the bearing clearance.All this can lead to so-called "marks" of the clamping bells on the optical surfaces of the workpieces to be clamped and other surface damage, which of course must be avoided.

[0006] From the publication DE-A-100 08 710, a centering machine is known in which a pivotable rocker arm is provided, at one end of which the axially movable centering spindle is pivoted, and at the other end of which a counterweight is pivoted to generate a torque on the rocker arm that counteracts the torque generated by the axially movable centering spindle. A combined lifting and clamping device engages at the end of the rocker arm to which the counterweight is pivoted. In addition to a spring mechanism, this device has a ball screw drive driven by an electric motor. This ball screw drive serves to move one centering spindle relative to the other centering spindle in an axial direction under CNC control in order to align the workpiece between the clamping bells (contacting and alignment phases) and, via the spring mechanism, to clamp it (clamping phase).This state of the art also provides a machining unit for edge machining of the workpiece once it has been clamped, but this is not described in detail.

[0007] Although the mechanism consisting of a rocker arm and counterweight in this state-of-the-art technology allows for a sensitive probing or clamping movement of the axially movable centering spindle toward the workpiece to be clamped with very low and easily controllable forces, it has the disadvantage that a certain transverse force is introduced into the clamping spindle via the rocker arm, resulting in radial heat buildup, which can ultimately impair the axial alignment of the centering spindle shafts. The same applies to the rotary drive of the centering spindle shafts, which is achieved here via gear pairs acting on one side.

[0008] Furthermore, the document DE-A-29 40 901 discloses an edge grinding machine (so-called "edger") for ophthalmic lenses, in which a ophthalmic lens is held between two half-shafts by means of "holding means". Of these half-shafts, the first half-shaft is rotationally driven and not longitudinally adjustable, and the second half-shaft is rotationally and longitudinally adjustable, but not driven. Furthermore, the second half-shaft is connected to a cylinder-piston unit via a piston rod, so that the second half-shaft can be driven as a result of a displacement of the piston rod protruding from the cylinder-piston unit. The cylinder-piston unit has two coaxially arranged (tandem arrangement) pistons connected to one another by means of a further piston rod, each with different effective areas, which both act on the piston rod. Thus, the second half-shaft can be actuated via the piston rod with two different forces for displacing the second half-shaft or the second half-shaft.to hold the lens during the grinding process. This simple device is intended to eliminate the risk of damage to the lens or injury to the operator when moving the second half-shaft. However, this state of the art does not provide essential features for the "bell clamping method" described above for centering lenses in precision optics, such as two clamping bells or two rotating centering spindles.

[0009] Finally, for motion tasks involving both rotating and reciprocating movements, an electric motor consisting of stator and rotor components along with bearings is known from DE-A-29 06 404. A special feature of this electric motor is that both the armature of a rotating field motor and the armature of a linear motor are arranged one behind the other on a common shaft, with the stator of a rotating field motor and the linear comb of a linear motor assigned to them. This prior art does not contain any reference to optical centering machines. TASK

[0010] The invention is based on the object of designing a centering machine for workpieces, particularly for optical lenses with curved optical surfaces, in such a way that the problems mentioned above regarding the prior art are addressed. In particular, the centering machine should enable an optimized bell clamping process, in which so-called "marks" and other surface damage on the usually sensitive surfaces of the workpieces to be clamped and machined are reliably avoided due to the usually very hard and sharp-edged contact areas of the centering or clamping bells. DESCRIPTION OF THE INVENTION

[0011] This object is achieved by the features specified in patent claim 1. Advantageous or expedient developments of the invention are the subject of patent claims 2 to 13.

[0012] According to the invention, a centering machine for workpieces, namely optical lenses with curved optical surfaces, comprises two centering spindles, the centering spindle shafts of which are each driven in rotation and accommodated in centering spindle housings, are axially aligned with respect to a centering axis and each accommodate a cup-shaped clamping bell at the mutually facing clamping bell ends, a lifting device by means of which one of the centering spindle shafts can be sensitively axially advanced with respect to the other of the centering spindle shafts along the centering axis in order to align one of the workpieces between the clamping bells in a bell clamping process, in which the clamping bells apply slight pressure to the workpiece in a contact phase before the workpiece is automatically displaced in a direction transverse to the centering axis in an alignment phase due to the curvature of its optical surfaces until it has assumed a position between the clamping bells,which enables the minimum distance between the clamping bells under the given geometric conditions, a clamping device for applying a clamping force to one of the centering spindle shafts in order to clamp the workpiece aligned between the clamping bells in a clamping phase following the alignment phase, and at least one machining unit movable relative to the centering axis and having a tool for edge machining of the workpiece clamped between the clamping bells, with the special feature that the centering spindle shaft, which can be axially advanced via the lifting device, can be driven in rotation by means of a rotary drive which, like the lifting device, is arranged coaxially with respect to the centering axis, so that due to the arrangement of the rotary drive on the centering spindle shaft centered with respect to the centering axis, only a torque about the centering axis can be generated without introducing a transverse force into the centering spindle shaft.

[0013] Due to the coaxial arrangement of the lifting device and the rotary drive for the axially adjustable centering spindle shaft on one and the same axis, namely the centering axis, these devices ensure that during the bell clamping process, when the centering spindle shafts are optionally driven in rotation, particularly during the alignment phase of the bell clamping process, no (one-sided) transverse force is introduced into the corresponding centering spindle shaft either in connection with the axial adjustment of the corresponding centering spindle shaft or the axial force introduction into the corresponding centering spindle shaft, or in connection with the rotary drive of the corresponding centering spindle shaft. Due to the arrangement of the rotary drive centered with respect to the centering axis, only a torque about the centering axis is generated on the corresponding centering spindle shaft. As a result, there is no risk of transverse displacement orTilting and / or bending moments on the corresponding, rotating centering spindle shaft, which could jeopardize the precise axial alignment of the centering spindle shafts and their concentricity and axial runout. Furthermore, the coaxial arrangement of the lifting device and rotary drive means that these assemblies pose no risk of heat buildup in the radial direction relative to the centering axis. As a result, "marks" and other surface damage to the workpieces to be clamped and machined, which could occur due to intolerable radial and / or axial runout of the clamping or centering bells due to insufficient axial alignment of the rotating centering spindle shafts, are reliably avoided.In addition, the space required by the arrangement in the radial direction relative to the centering axis is advantageously small, which promotes good accessibility of the workpiece clamped between the clamping bells during its machining.

[0014] Furthermore, the lifting device and the clamping device are preferably arranged coaxially with respect to the centering axis. Because the lifting device and the clamping device are then also located on one and the same axis, namely the centering axis, no transverse force is introduced via these devices during the bell clamping process, particularly in the clamping phase thereof, in conjunction with the axial feed of the corresponding centering spindle shaft or the axial force introduction into the corresponding centering spindle shaft, which could generate a transverse displacement, tilting and / or bending moments on the corresponding centering spindle shaft, which would endanger the precise axial alignment of the centering spindle shafts and their concentricity and axial runout. Furthermore, the coaxial arrangement of the lifting device and the clamping device also means that these devices do not pose a risk of heat generation in the radial direction relative to the centering axis.As a result, excessive radial and / or axial runout (greater than 1 to 2 µm) resulting from the axial force introduction into or axial feed of the corresponding centering spindle shaft on the highly precisely ground clamping surfaces of the clamping or centering bells can be reliably avoided, thus preventing "marks" and other surface damage on the workpieces to be clamped and machined. A further advantage of the coaxiality or - viewed along the centering axis - concentricity of the lifting device and clamping device is that this arrangement is very close to the centering axis, i.e., very compact in the radial direction relative to the centering axis, so that at least one machining unit or its tool can easily reach the workpiece clamped between the clamping bells, without requiring any major fixture-related expenditure.

[0015] For example, a commercially available linear motor in synchronous, asynchronous, or double-comb design could be used for the lifting device, possibly with a lightweight stator and actuator made of carbon fiber-reinforced plastic parts. It is preferred, however, for the lifting device to have a voice coil actuator operatively connected to the axially adjustable centering spindle shaft, which comprises at least one coil coaxial with the centering axis and at least one permanent magnet interacting with the coil. The advantages of such a voice coil drive are, in particular, that due to its coaxially rotationally symmetrical design with respect to the centering axis, it is very compact, has only small moving masses, and allows very sensitive control of the feed force, particularly during the probing and alignment phases of the bell clamping process.

[0016] Although the moving coil drive can in principle be designed with a stationary magnet and a moving coil (moving coil design), the permanent magnet is preferably attached to a rotor part that is connected to the axially adjustable centering spindle shaft, while the coil surrounding the permanent magnet is mounted in a machine-fixed moving coil drive housing (moving magnet design). This makes powering the moving coil drive and cooling it particularly easy. The permanent magnet can then be very short in the axial direction, i.e., significantly shorter than the coil, so that the feed forces of the moving coil drive are advantageously essentially uniform over the entire required stroke.

[0017] In further pursuing the inventive concept, the clamping device can have an annular piston mounted on the axially adjustable centering spindle shaft. On its side facing away from the clamping bell end of the axially adjustable centering spindle shaft, it forms an annular active surface. This annular chamber defines an annular chamber in the centering spindle housing, through which the annular piston can be pneumatically actuated to generate the clamping force. This design enables simple, effective and very sensitive control of the clamping force during the clamping phase of the bell clamping process and secure holding of the workpiece during its machining.

[0018] In principle, the clamping spindle and fixed spindle can be arranged anywhere in space, as long as the coaxiality of the spindle shafts is ensured, e.g. in a horizontal orientation or in a vertical orientation, with an upper fixed spindle and a lower clamping spindle, as disclosed in the document DE-A-37 44 118. However, a configuration is preferred in which the centering spindle with the axially adjustable centering spindle shaft is arranged above the other centering spindle, wherein the annular piston forms a further annular active surface on its side facing the clamping bell end of the axially adjustable centering spindle shaft, which delimits a further annular chamber in the centering spindle housing, via which the annular piston can be pneumatically acted upon in order to ensure pneumatic weight compensation on the axially adjustable centering spindle shaft.

[0019] A vertical arrangement of the centering spindles is advantageous in that it makes automated workpiece loading much easier because the workpiece placed on the lower clamping bell remains in place - unlike with a horizontal arrangement of the centering spindles. With such a vertical arrangement of the centering spindles, designing the lower centering spindle as a fixed spindle and the upper centering spindle as a clamping spindle also has the particular advantage that gravity helps lower the clamping spindle, thus reducing the likelihood of stick-slip effects on the bearings / guides, which would otherwise make the axial spindle movement uneven. For sensitive infeed, however, the weight of the clamping spindle and the clamping bell mounted on it must be counteracted or compensated for, which can be achieved in a simple manner using pneumatic weight compensation.

[0020] Such a pneumatic weight compensation also has the advantage - compared to, for example, a weight compensation with a counterweight, as disclosed in the document DE-A-100 08 710 - that a changing total weight of spindle and clamping bell due to the use of different clamping bells can easily be taken into account.

[0021] Particularly advantageous here is the aforementioned use of the annular piston with its annular effective surfaces in a double-acting (ring) piston (ring) cylinder arrangement, which, due to its coaxial position with respect to the centering axis and the use of only one annular piston, is not only very compact in both the radial and axial directions, but also ensures that no transverse forces are exerted on the corresponding centering spindle shaft when the clamping force is applied or when the weight of the clamping spindle and clamping bell is counteracted.

[0022] In principle, the annular piston can be designed with seals, which would have the advantage of low compressed air consumption. However, a sealless design of the annular piston is preferred, which prevents any stick-slip effects as well as seal wear on the annular piston. A slight compressed air leakage around the piston circumference also enables more precise pressure control using, for example, a servo pressure control valve, with improved control hysteresis, because excessive pressure does not have to be released at the valve itself.

[0023] In an advantageous embodiment of the centering machine, the rotary drive can be designed as an internal rotor torque motor, with a stator mounted in the centering spindle housing and a rotor that is always surrounded by the stator and attached to the outer circumference of the axially adjustable centering spindle shaft. The rotor is longer than the stator and, together with the axially adjustable centering spindle shaft, can be axially displaced relative to the stator. The advantages of the torque motor are, in particular, that, due to its design—unlike a conventional three-phase asynchronous or stepper motor—a torque motor exhibits only minimal cogging (jerking during rotation caused by magnetic forces) and can directly generate high torque and holding torques with high positioning accuracy. This ensures excellent synchronous operation of the centering spindle shafts even during machining of the workpiece clamped between the clamping bells.a good fixation against unintentional twisting.

[0024] In principle, plain bearings or magnetic bearings can be used for the axial and rotational support of the axially adjustable centering spindle shaft. However, to minimize bearing clearance, avoid stick-slip effects, and minimize wear while maintaining reasonable cost, it is preferred that the axially adjustable centering spindle shaft be axially displaceable and rotatably mounted in the centering spindle housing by means of an air bearing arrangement. The air bearing arrangement preferably comprises at least two air bearing sections, with the rotary drive arranged axially between the air bearing sections, thus ensuring high rigidity of the guide.

[0025] Advantageously, a runout measuring device can be integrated into the centering machine to monitor the centering or to check the alignment of the workpiece after the bell clamping process. This device can be used to measure the axial position of an end face edge region of the workpiece clamped between the clamping bells in a direction parallel to the centering axis. Such a cost-effective measuring device can be provided as an alternative to or in addition to a conventional laser centering device and is particularly advantageous when centering workpieces with highly reflective or poorly translucent surfaces, where laser centering devices reach their limits.

[0026] The runout measuring device preferably comprises a tactile probe that can be moved together with the machining unit for positioning relative to the end face edge area on the workpiece to be scanned. Compared to other conceivable non-contact sensors, such as optical sensors, the advantages here are that such tactile probes are robust, offer good value for money, and operate independently of the material properties (e.g., reflective or absorbent) of the workpiece. Even minor contamination (such as coolant droplets) on the workpiece surfaces to be scanned does not pose any problems. Since the tactile probe can also be moved together with the machining unit, the runout measuring device advantageously requires no additional axes of movement.

[0027] Finally, in a suitable embodiment, the probe of the axial runout measuring device can be movable with respect to the machining unit from a protected parking position behind the tool into a measuring position protruding from the tool and vice versa, so that the probe is protected during the actual edge machining and there is no risk of collision with the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention is explained in more detail below using a preferred embodiment of a centering machine with reference to the attached, partially simplified or schematic drawings. To simplify the illustration, in addition to parts of the centering machine casing, the operating unit and control system, disks, storage areas for workpieces and tools, the supply devices (including lines, hoses, and pipes) for power, compressed air, and cooling lubricant, the cooling lubricant return line, as well as the measuring, maintenance, and safety devices have mostly been omitted from the drawings, at least to the extent that they are not necessary for understanding the invention. The drawings show: Fig. 1 a perspective view of a centering machine according to the invention for in particular optical lenses as workpieces from diagonally above / front right; Fig. 2 a scaled view compared to the Fig. 1 enlarged, broken perspective view of the centering machine according to Fig. 1 from diagonally above / right side; Fig. 3 a front view of the centering machine according to Fig. 1 ; Fig. 4 a perspective view of the centering machine according to Fig. 1 from above / behind; Fig. 5 a perspective view of an upper centering spindle assembly of the centering machine according to Fig. 1 in a representation otherwise isolated from the centering machine, with a clamping bell (below) which is mounted on a centering spindle shaft mounted in a centering spindle housing; Fig. 6 a longitudinal sectional view of the upper centering spindle assembly according to Fig. 5 ; Fig. 7 an enlarged view of detail VII in particular showing an electric lifting device for the centering spindle shaft Fig. 6 ,with additionally indicated compressed air supply for an air bearing arrangement for supporting a measuring head on the centering spindle shaft; Fig. 8 an enlarged view of detail VIII in particular showing an electric rotary drive and a combined pneumatic clamping and weight compensation device for the centering spindle shaft Fig. 6 , with additionally indicated compressed air supply for an upper air bearing section of an air bearing arrangement for supporting the centering spindle shaft in the centering spindle housing; Fig. 9 an enlarged view of the detail IX, showing in particular the clamping bell receptacle on the centering spindle shaft in Fig. 6 , with additionally indicated compressed air supply for a lower air bearing section of the air bearing arrangement for supporting the centering spindle shaft in the centering spindle housing; Fig. 10 a longitudinal sectional view of the upper centering spindle assembly according to Fig. 5 , with indicated power supply for the lifting device and compressed air supply / valve arrangement for the combined pneumatic clamping and weight compensation device, in a state after weight compensation in preparation for a bell clamping process; Fig. 11 one of the Fig. 10 similar longitudinal section view of the upper centering spindle assembly according to Fig. 5 , with the clamping bell lowered onto an optical lens after the probing phase of the bell clamping process during the alignment phase of the bell clamping process; Fig. 12 a Fig. 10 and 11 similar longitudinal section view of the upper centering spindle assembly according to Fig. 5 , in a state during the clamping phase of the bell clamping process; Fig. 13 a perspective view of a Fig. 1 and 3 left-hand machining unit of the centering machine, comprising a grinding spindle with a grinding wheel rotatably mounted thereon, according to Fig. 1 in a representation otherwise isolated from the centering machine, to illustrate a cooling lubricant supply device for supplying a cooling lubricant to the grinding wheel; Fig. 14 an enlarged sectional view in particular of the cooling lubricant supply device according to Fig. 13 according to the section line XIV-XIV in the Fig. 3 and 13 ; Fig. 15 an enlarged sectional view of the cooling lubricant supply device according to Fig. 13 according to the section line XV-XV in Fig. 14 ; Fig. 16 an enlarged sectional view of the cooling lubricant supply device according to Fig. 13 according to the section line XVI-XVI in Fig. 14 ; and Fig. 17 to 19perspective views of the Fig. 1 and 3 right machining unit of the centering machine according to Fig. 1 in a representation otherwise isolated from the centering machine, without splash guard and cooling lubricant supply device, to illustrate the operation of a runout measuring device integrated in the centering machine for checking the centering of the optical lens held between the clamping bells - as also schematically indicated in these figures. DETAILED DESCRIPTION OF THE EMBODIMENT

[0029] In the Fig. 1 bis 4 is a CNC-controlled centering machine for workpieces, namely optical lenses L numbered 10. The centering machine 10 has a machine bed 12 made of polymer concrete, which has a Fig. 1 front receiving space 14 for a lower centering spindle assembly 16, which is fixedly mounted on the machine bed 12. In the receiving space 14, a bridge-like portal 18 is supported on the machine bed 12, which extends upwards over the latter and carries at a central location an upper centering spindle assembly 20, which will be described below with reference to the Fig. 5 bis 12 will be described in detail later. The lower centering spindle assembly 16 comprises a lower centering spindle 22 (fixed spindle), whose axially fixed lower centering spindle shaft 24, which is rotatably driven about a workpiece rotation axis C1 by an internal rotor torque motor (not shown), is mounted by air bearings (not shown) in a lower centering spindle housing 26, which in turn is fastened to the machine bed 12 by a surrounding housing 28.

[0030] As will be explained in more detail, the upper centering spindle assembly 20 initially comprises an upper centering spindle 30 (clamping spindle) with an upper centering spindle housing 32, in which an upper centering spindle shaft 34, which can be driven to rotate about a workpiece rotation axis C2, is accommodated in an axially displaceable manner. The upper centering spindle 30, with its centering spindle housing 32, passes through a central opening in the portal 18, with which the centering spindle housing 32 is connected from below via a bearing ring 35 (in Fig. 9 omitted). The lower centering spindle shaft 24 and the upper centering spindle shaft 34 are arranged such that they are axially aligned with respect to a vertically extending centering axis C, and are each designed at the mutually facing ends to receive a clamping bell 36, 38, as known from the German standard DIN 58736-3 mentioned above. Both centering spindle shafts 24, 34 can be driven independently of one another in a rotational angle-controlled manner about the workpiece rotation axes C1, C2; synchronous operation of the centering spindle shafts 24, 34 is achieved by CNC technology. To securely hold the clamping bells 36, 38 without play, each centering spindle shaft 24, 34 is provided at its end with a known hydraulic expansion chuck 40, 42.

[0031] Furthermore, the upper centering spindle assembly 20 comprises, in particular, the Fig. 6 bis 9 general - seen in a sequence from top to bottom in the figures; described in detail later - (i) a lifting device 44, by means of which the upper centering spindle shaft 34 can be sensitively axially adjusted relative to the lower centering spindle shaft 24 along the centering axis C (position-controlled clamping bell linear axis W) in order to align the optical lens L between the clamping bells 36, 38, (ii) a measuring system 46 for detecting the axial position and the angular position of the upper centering spindle shaft 34 relative to the upper centering spindle housing 32, (iii) a rotary drive 48, by means of which the upper centering spindle shaft 34, which can be axially adjusted via the lifting device 44, can be driven in rotation, (iv) a pneumatic clamping and weight compensation device 50 - combined in the illustrated embodiment - which serves in particular to apply a clamping force to the upper centering spindle shaft 34 in order to align the optical lens L between the clamping bells 36,38 aligned optical lens L, and an air bearing arrangement 52 with two air bearing sections 54, 56 for the upper centering spindle shaft 34, wherein the rotary drive 48 and the clamping and weight balancing device 50 are located axially between the air bearing sections 54, 56, with the special feature that the lifting device 44, the rotary drive 48 and the clamping and weight balancing device 50 are arranged coaxially with respect to the centering axis C.

[0032] As continues to be the case, in particular Fig. 1 bis 4 As can be seen, the centering machine 10 has two machining units 58, 60 which are movable relative to the centering axis C, each having a grinding wheel G as a tool for edge machining of the optical lens L clamped between the clamping bells 36, 38. Both machining units 58, 60 can be moved independently of one another in a working space 62 which is delimited laterally and upwardly by the gantry 18 and into which the two centering spindles 22, 30 with their clamping bells 36, 38 also protrude from below and above, respectively, in a direction parallel to the centering axis C (position-controlled tool linear axis Z1 or Z2) and in a direction perpendicular thereto (position-controlled tool linear axis X1 or X2).The movement mechanism for this comprises two "tilted" cross table arrangements arranged and formed mirror-symmetrically with respect to an imaginary plane containing the centering axis C, each with a driven X-slide 64, 64' and a driven Z-slide 66, 66'.

[0033] More precisely, in the Fig. 1 bis 3 Behind the portal 18 and parallel thereto, two guide rails 68, 70 are mounted on the machine bed 12, which also run parallel to each other. These guide rails serve for the axial guidance of both X-slides 64, 64'. For this purpose, each X-slide 64, 64' is equipped with two pairs of guide carriages 72, 72', one pair of which engages with one guide rail 68 and the other pair with the other guide rail 70. For the linear drive of the X-slides 64, 64', which are guided on the guide rails 68, 70 provided with rubber-buffered (not shown in detail) end stops 74, a linear motor 76 is provided for each slide (only for the Fig. 1 and 2 right X-slide 64'), each with a stator 78 (magnets) mounted from above on the machine bed 12 and a rotor 80 (coils) mounted from below on the respective X-slide 64, 64', as best seen in Fig. 2 can be seen.

[0034] A bracket 82, 82' is screwed onto each X-slide 64, 64' from above, on which the respective Z-slide 66, 66' is guided. For this purpose, two pairs of guide carriages 84, 84' are mounted in parallel on the respective bracket 82, 82' on the end face facing the gantry 18. These pairs engage with guide rails 86, 86' mounted in pairs parallel to each other on each Z-slide 66, 66'. For the linear drive of each Z-slide 66, 66', a servo motor 88, 88' is provided. This servo motor is flanged to the respective bracket 82, 82' from above and drives a threaded spindle (not shown) that engages with a threaded nut on the slide side (also not shown). On each Z-slide 66, 66', a spindle block 90, 90' is mounted facing the portal 18, on which a grinding spindle 92, 92' of the respective machining unit 58, 60 with its grinding spindle housing 94, 94' is mounted.Each grinding spindle 92, 92' comprises, in a manner known per se, an electric rotary drive (not shown in detail) for the respective grinding wheel G.

[0035] The following can be seen in the Fig. 1 , 3 and 4 Finally, a splash guard 96, 96' mounted on each grinding spindle housing 94, 94', which surrounds the respective grinding wheel G except for an engagement area for the edge machining of the optical lens L, and on each machining unit 58, 60, a cooling lubricant supply device 98, 98', which is mounted on the respective grinding spindle housing 94, 94' via the splash guard 96, 96' and is subsequently controlled by means of the Fig. 13 bis 16 will be described in detail. In addition, the Fig. 3 and 4 parts of a runout measuring device 100 for checking the centering can also be seen, which is flanged to the spindle bracket 90' from below in the machining unit 60 and will be described later with reference to the Fig. 17 bis 19 will be explained in more detail.

[0036] In the Fig. 5 bis 9 Further details of the upper centering spindle assembly 20 can be seen. According to the Fig. 6 and 7 The lifting device 44 has a moving coil drive 102 operatively connected to the axially adjustable upper centering spindle shaft 34, which comprises one (or more) coil(s) 104 coaxial with respect to the centering axis C and at least one permanent magnet 106 cooperating with the coil 104. While the permanent magnet 106 is attached to a rotor part 108, which is firmly connected to the axially adjustable upper centering spindle shaft 34 via a screw connection 110 so that it can rotate together with the upper centering spindle shaft 34, the coil 104 surrounding the permanent magnet 106 is mounted in a machine-fixed moving coil drive housing 112, which in turn surrounds the coil 104. Fig. 7 The essentially hollow cylindrical moving coil drive housing 112 is closed at the top with a housing cover 114 screwed to it. From below in Fig. 7 an annular flange plate 116 is screwed to the voice coil drive housing 112 (the screws are not shown), through which the rotor part 108 extends.

[0037] The plunger coil drive housing 112 with the coil 104, the housing cover 114 and the flange plate 116 is supported relative to the upper centering spindle housing 32 via a drive holder 118, which is best Fig. 5 can be seen. The drive holder 118 comprises an upper annular disc 120 and a lower annular disc 122, which are connected to one another via two webs 124, 126, which run parallel to the centering axis C and - with respect to the centering axis C - are diametrically opposite one another. The moving coil drive housing 112 extends through the upper annular disc 120 of the drive holder 118 and is firmly connected to it via the flange plate 116, which is flanged to the upper annular disc 120 from below by means of screws (also not shown).

[0038] The measuring system 46 for detecting the axial and angular positions of the upper centering spindle shaft 34 is accommodated in the free space between the annular discs 120, 122 and the webs 124, 126 of the drive holder 118. The measuring system 46 comprises, in particular, Fig. 5 an axial measuring head 128, which cooperates in a manner known per se with a measuring tape 130 in order to detect the axial position of the upper centering spindle shaft 34 with respect to the centering spindle housing 32, and an angle measuring head 132, which cooperates in a manner known per se with a measuring ring 134 (see the Fig. 6 and 7 ) to detect the angular position of the upper centering spindle shaft 34 about the centering axis C.

[0039] While the measuring tape 130 on the Fig. 5 left web 124 of the drive holder 118, almost completely bridging the free space between the ring disks 120, 122 of the drive holder 118, the axial measuring head 128 is attached to a measuring head carrier 138 via a measuring head adapter 136. The angle measuring head 132 is also attached to the measuring head carrier 138. The measuring ring 134, however, is according to the Fig. 6 and 7attached to a measuring ring carrier 140 which is connected to an upper shoulder 142 of the upper centering spindle shaft 34 in a rotationally fixed manner.

[0040] The measuring head carrier 138 is mounted relative to the upper centering spindle shaft 34 via a combined axial / radial air bearing arrangement 144, which according to Fig. 7 on a bearing ring 145 screwed to the measuring head carrier 138, an annular porous axial bearing pad 146 and on the inner circumference of the measuring head carrier 138, a porous radial bearing bush 148. As in Fig. 7 Also shown is the axial bearing pad 146 and the radial bearing bushing 148 of the axial / radial air bearing assembly 144 connected to a compressed air source Q, wherein the axial bearing pad 146 supports the measuring head carrier 138 relative to the measuring ring carrier 140, while the radial bearing bushing 148 supports the measuring head carrier 138 on the upper shoulder 142 of the centering spindle shaft 34. In Fig. 5 Finally, at 150, an air-bearing anti-rotation device is indicated, over which the measuring head carrier 138 on the Fig. 5 right web 126 of the drive holder 118 is rotatably supported.

[0041] It can be seen that the measuring head carrier 138, together with the upper centering spindle shaft 34, can move very smoothly in the axial direction relative to the machine-mounted centering spindle housing 32. However, due to its torque support relative to the drive holder 118, the rotary movement of the centering spindle shaft 34 does not follow or impede it. In this respect, the measuring system 46 allows for very precise and sensitive detection of the axial and angular positions of the upper centering spindle shaft 34 relative to the centering spindle housing 32.

[0042] According to the Fig. 5 , 6and in particular Fig. 8, the drive holder 118 is flanged with its lower annular disk 122 onto an annular bearing flange 152, which in turn is screwed to the centering spindle housing 32 (the connecting means are again not shown) and closes it at the top. The upper air bearing section 56 of the air bearing arrangement 52 for the centering spindle shaft 34, which is connected to the compressed air source Q, is fastened in the form of a porous radial bearing bush to the inner circumference of the bearing flange 152. The lower air bearing section 54 of the air bearing arrangement 52, which is also connected to the compressed air source Q, is best seen in Fig. 9 This is also a porous radial bearing bushing that is mounted in a tapered, lower section of the centering spindle housing 32. Accordingly, the axially adjustable upper centering spindle shaft 34 is mounted in the centering spindle housing 32 by means of the air bearing arrangement 52 in such a way that it can be axially displaced and rotated very easily relative to the centering spindle housing 32. As already indicated above, the rotary drive 48 for this purpose, as well as the clamping and weight compensation device 50 acting on the centering spindle shaft 34, are accommodated in a coaxially aligned arrangement between the air bearing sections 54, 56 in the centering spindle housing 32.

[0043] The rotary drive 48 is an internal rotor torque motor with a stator 154 (winding) mounted in the centering spindle housing 32 and a rotor 156, which is always surrounded by the stator 154 and fastened to the outer circumference of the axially adjustable upper centering spindle shaft 34. The rotor 156 is significantly longer in the axial direction than the stator 154 and, together with the centering spindle shaft 34, is axially displaceable relative to the stator 154. According to Fig. 8 The rotor 156 comprises a rotor sleeve 158 fastened to the centering spindle shaft 34, which in turn carries the magnets 160 of the rotary drive 48 on its outer circumference, which are cast with the rotor sleeve 158 using a plastic or resin. Axially in the region of the upper air bearing section 56 of the air bearing arrangement 52, the rotor sleeve 158 and the magnets 160 are also firmly surrounded by a thin bearing sleeve 162 of the rotor 156.

[0044] The clamping and weight compensation device 50 is arranged in the centering spindle housing 32 below the rotary drive 48. As best shown in the Fig. 6 and 8As can be seen, the clamping and weight compensation device 50 has a sealless annular piston 164 which is mounted on the outer circumference of the axially adjustable centering spindle shaft 34 directly below the rotor 156 of the rotary drive 48 and leaves only a small annular gap (not visible in the figures) to a cylinder wall 165 in the centering spindle housing 32. The annular piston 164 forms, on its side facing away from the clamping bell end of the upper centering spindle shaft 34, an annular active surface 166 which, in the centering spindle housing 32, delimits an annular chamber 168 adjacent to the stator 154 of the rotary drive 48, via which annular piston 164 can be pneumatically actuated in order to generate the clamping force - acting downwards in the figures.On its side facing the clamping bell end of the upper centering spindle shaft 34, the annular piston 164 forms a further annular active surface 170, which is larger than the active surface 166 for clamping and delimits a further annular chamber 172 in the centering spindle housing 32, via which the annular piston 164 can be pneumatically actuated in order to ensure pneumatic weight compensation on the upper centering spindle shaft 34 - with the force direction upwards in the figures. The compressed air supply for the annular chambers 168, 172 of the clamping and weight compensation device 50 is only in the . Fig. 10 bis 12 shown schematically (compressed air source Q, servo pressure control valves V1, V2). Pressure gauges also indicated here are intended to indicate when which annular chamber 168 or 172 is pneumatically pressurized during the bell clamping process.

[0045] The Fig. 9 finally shows that in Fig. 6 lower clamping bell end of the upper centering spindle shaft 34. The clamping bell 38 and the hydraulic expansion chuck 42 for receiving the clamping bell 38 are sufficiently known, so that these parts require no further explanation. The hydraulic expansion chuck 42 is firmly connected to the centering spindle shaft 34 via a connecting ring 174 with a labyrinth seal to the centering spindle housing 32. Furthermore, the Fig. 5 bis 12 Reference numeral 176 denotes a through-bore which extends from the housing cover 114 of the moving coil drive housing 112 to the clamping bell 38 and, in a manner known per se, enables the optional use of a laser centering device (not shown).

[0046] The sequence of a bell clamping process will now be described using the Fig. 10 bis 12 will be briefly explained, in which only the hydraulic expansion chuck 40 with the lower clamping bell 36 held thereon is shown from the lower centering spindle or its centering spindle shaft 24.

[0047] For a sensitive feed of the clamping bell 38 over the upper centering spindle shaft 34, the weight of the centering spindle shaft 34 with the clamping bell 38 attached to it and all parts moving axially along the centering axis C - hydraulic expansion chuck 42, connecting ring 174, annular piston 164 of the clamping and weight compensation device 50, rotor 156 of the rotary drive 48, measuring ring carrier 140 and measuring head carrier 138 with the components of the measuring system 46 attached to it, rotor part 108 and permanent magnet 106 of the lifting device 44 - must first be compensated. For this purpose, the annular chamber 172 of the tensioning and weight compensation device 50 is subjected to a sensitively controlled fluid pressure via the servo pressure control valve V2, which acts on the lower active surface 170 of the annular piston 164 so that the piston lifts the aforementioned components.The fluid pressure is controlled with the plunger coil drive 102 deactivated so that the centering spindle shaft 34 performs almost no vertical movement and is held in suspension. The vertical movement is detected by the measuring system 46 integrated in the centering spindle assembly 20, with a preselected threshold value for a residual speed of the vertical movement limiting this control process. The fluid pressure, now regulated via the servo pressure control valve V2 in the lower annular chamber 172, is kept constant for the rest of the process. The initial state after weight compensation is shown in . Fig. 10 shown.

[0048] The probing phase of the bell clamping process can now begin, in which the upper clamping bell 38 is moved towards the lower clamping bell 36 in order to come into contact with the lens L placed on the lower clamping bell 36. For this purpose, the plunger coil drive 102 of the lifting device 44 is energized via the current regulator S in order to lower the upper clamping bell 38 with a very sensitively adjustable force and a clearly defined path until the upper clamping bell 38 rests on the lens L (end of the probing phase).

[0049] The centering spindle shafts 24, 34 can then be driven to rotate around the centering axis C, whereby the lens L - if necessary with the addition of a lubricant - slides more easily into position, with its two radius surfaces resting against the annular cutting edges of the clamping bells 36, 38 (end of the alignment phase). This state is in Fig. 11 shown.

[0050] After the lens L is thus aligned to its optical axis, the moving coil drive 102 of the lifting device 44 is operated according to Fig. 12 switched off again. At the same time, the clamping force is increased in a defined manner by pressurizing the upper annular chamber 168 of the clamping and weight compensation device 50 and thus the upper active surface 166 of the annular piston 164 via the servo pressure control valve V1 to such an extent that the lens L is securely clamped for the edge grinding process, which can now be carried out with the aid of the processing units 58, 60.

[0051] It is evident that during the bell clamping process, due to the coaxial arrangement of the actuators acting on the upper centering spindle shaft 34 (lifting device 44, rotary drive 48, clamping and weight compensation device 50), no transverse forces are generated that could endanger the axial alignment of the centering spindle shafts 24, 34.

[0052] The actual edge machining, in which the edge of the lens L clamped between the clamping bells 36, 38 is ground by means of the rotatingly driven grinding wheels G on the grinding spindles 92, 92' of the machining units 58, 60, while the grinding spindles 92, 92' are moved in the linear axes X1, X2 and, if applicable, Z1, Z2 in accordance with the contour to be ground on the lens L, will not be explained in more detail here, since it is sufficiently known to the person skilled in the art.

[0053] As explained above with reference to the Fig. 1 , 3 and 4 As already mentioned, a cooling lubricant supply device 98, 98' for the respective grinding wheel G is provided on each processing unit 58, 60, which is subsequently used for the Fig. 1 left processing unit 58 based on the Fig. 13 bis 16 will be explained in more detail. The cooling lubricant supply device 98' at the Fig. 1 The right-hand machining unit 60 is mirror-symmetrical to the left-hand cooling lubricant supply device 98 and will therefore not be described separately.

[0054] As in particular the Fig. 14 and 16show, the cooling lubricant supply device 98 - which can in principle also be used on other grinding machines - generally has a feed shoe 178 which is held indirectly on the grinding spindle housing 94 in a manner to be described below and sits on a circumferential surface U of the grinding wheel G. The feed shoe 178 is made of a machinable material, preferably plastic. The feed shoe 178 has a seating surface 180 facing the grinding wheel G, which has a shape essentially complementary to the circumferential surface U of the grinding wheel G, for which purpose the seating surface 180 is preferably ground into the feed shoe 178 by means of the grinding wheel G as a negative contour of the circumferential surface U of the grinding wheel G. Essentially in the center, the feed shoe 178 is provided with a pocket-like recess 182 into which the cooling lubricant can be fed under pressure.Furthermore, a spring mechanism 184 is provided, by means of which the feed shoe 178 is pretensioned with its seat surface 180 against the circumferential surface U of the grinding wheel G, wherein in the illustrated embodiment the pretensioning force of the spring mechanism 184 can be adjusted, as will be explained below.

[0055] According to the Fig. 13 and 14 The cooling lubricant supply device 98 is held on the splash guard 96, which in turn is attached to the grinding spindle housing 94. For this purpose, the splash guard 96 has an extension 186 (see Fig. 14 ), which carries a holder 188 of the cooling lubricant supply device 98. In Fig. 14 the bracket 188 is provided on the left with a stepped through-hole 190 for receiving a control slide 192, on which Fig. 15 also an L-connector 194 for the supply of cooling lubricant is connected. From above into the Fig. 14 and 15A stepped transverse bore 196 opens into the through bore 190, in which a hanger 198 for a shoe holder 200 is fastened, which in turn carries the feed shoe 178. Connecting bores 202, 204, 206, 208 in the control slide 192, hanger 198, shoe holder 200, and feed shoe 178, respectively, ensure a fluid connection between the L-shaped plug-in fitting 194 and the recess 182 in the feed shoe 178, with O-rings 210, 212, 214, 216 sealing against the environment. The flow rate of the cooling lubricant can be regulated via a control slide opening 218 by rotating the control slide 192 in the through hole 190 of the holder 188 via a handle 220 on the control slide 192.

[0056] According to in particular Fig. 14 the hanger 198 is provided at its end facing away from the control slide 192 with a ball head 222, which sits in an associated receptacle 224 in the shoe holder 200 and is secured there by means of an adjusting screw 226. The ball head 222 and the receptacle 224 thus form a joint located in front of the feed shoe 178, as seen in the direction of rotation D of the grinding wheel G, which is fixed to the grinding spindle housing and to which the feed shoe 178 is pivotally connected via the essentially tubular shoe holder 200, so that the feed shoe 178 can be placed essentially tangentially against the circumferential surface U of the grinding wheel G. A latch 228 held on the splash guard 96, which can be removed by means of a handle 230 for changing the feed shoe 178, forms a stop for the feed shoe 178 in the direction of rotation D of the grinding wheel G, which stop prevents the feed shoe 178 from being pulled along by the grinding wheel G.

[0057] Further details of the Fig. 14 The spring mechanism 184 held on the right side of the bracket 188 is the Fig. 16 can be removed. The spring mechanism 184 firstly has a stop pin 232, via which a force can be exerted on the feed shoe 178 in the direction of the grinding wheel G and which extends through a stepped through-bore 234 in the holder 188, wherein a lip ring 236 mounted in the through-bore 234 in the region of the end of the stop pin 232 protruding beyond the feed shoe 178 in the direction of the grinding wheel G ensures that the spring mechanism 184 does not otherwise become dirty.

[0058] The stop pin 232 is guided in a threaded sleeve 238 for axial displacement, wherein a helical compression spring 240 is provided radially between the stop pin 232 and the threaded sleeve 238, which spring is supported both on a step of the threaded sleeve 238 and on a step of the stop pin 232, so that it presses the stop pin 232 and the threaded sleeve 238 apart. In the operating state of the cooling lubricant supply device 98, however, the stop pin 232 is prevented by the feed shoe 178 from moving freely away from the threaded sleeve 238. z.B. If the feed shoe 178 is removed for maintenance work, a retaining ring 242 at the other end of the stop pin 232 prevents the spring mechanism 184 from falling apart.

[0059] The threaded sleeve 238, which is axially guided on the inner circumference of the through-bore 234 via an annular web, has an external thread 244 with which the threaded sleeve 238 is screwed into a nut 246, which in turn is firmly attached to the bracket 188. It can be seen that by rotating the threaded sleeve 238 via an adjusting wheel 248 attached to the threaded sleeve 238, the preload force of the helical compression spring 240 can be adjusted in a defined manner.

[0060] During operation of the cooling lubricant supply device 98, the cooling lubricant supply is first switched on, so that the cooling lubricant is fed under pressure via the L-shaped plug-in screw connection 194, the hanger 198, and the shoe holder 200 to the recess 182 in the feed shoe 178. The feed shoe 178 then acts as a hydrostatic plain bearing and lifts slightly from the circumferential surface U of the grinding wheel G. The bearing gap of this "hydrostatic bearing" can be adjusted by preloading the helical compression spring 240 in the spring mechanism 184. Practical testing of this cooling lubricant supply device 98 has shown that the cooling lubricant still surrounds the grinding wheel G, rotating at high speed, over an angle of more than 90° after leaving the "bearing pocket" or recess 182, and is only later, at larger angles, flung away from the grinding wheel G by the centrifugal forces acting on it.This unexpected effect allows the feed shoe 178 to be positioned relatively far away from the contact point between the grinding wheel G and the workpiece L, which in turn provides significant advantages in (among other things) workpiece handling. Furthermore, a "wandering" of the contact point between the workpiece L and the grinding wheel G caused by a non-circular outer contour of the workpiece L no longer poses problems for cooling or lubrication.

[0061] If necessary, for example, after the bell clamping process and before the actual edge machining, the centering of the lens L between the clamping bells 36, 38 can be carried out by means of the Fig. 3 be checked by the axial runout measuring device 100 integrated in the centering machine 10, which can detect the axial position of an end face edge region R of the lens L clamped between the clamping bells 36, 38 in a direction parallel to the centering axis C. Relevant details will be explained in more detail below with reference to the Fig. 17 bis 19 in which the splash guard 96' and the cooling lubricant supply device 98' have been omitted.

[0062] The runout measuring device 100 comprises a commercially available tactile probe 250, which extends parallel to the centering axis C and is movable for positioning with respect to the end face edge region R to be scanned on the workpiece L together with the machining unit 60, ie by means of the CNC axes X2, Z2, which in Fig. 18 illustrated by the corresponding movement arrows. Beforehand, the button 250 can be moved according to the corresponding movement arrow in Fig. 17 with respect to the processing unit 60 from a protected parking position ( Fig. 17 ) behind the grinding wheel G into a measuring position protruding from the grinding wheel G ( Fig. 18 & 19 ) are moved. For this purpose, a pneumatic cylinder 252 with end stops is flanged from below to the spindle bracket 90' of the machining unit 60. A piston rod 254, which can be optionally extended from the pneumatic cylinder 252, carries at its free end a holder 256 for the probe 250. The holder 256 is designed in the illustrated embodiment such that it can alternatively or additionally accommodate a further probe (not shown), in a position rotated by 90° relative to the probe 250, which would also enable control of the radial runout of the lens L clamped between the clamping bells 36, 38. The rotary movement arrow in Fig. 19 Finally, it indicates that the lens L is rotated about the centering axis C during the actual testing process, in which the probe 250 touches the end face edge region R on the lens L.

[0063] A centering machine for, in particular, optical lenses comprises two centering spindles whose rotatably driven centering spindle shafts are axially aligned with respect to a centering axis and are designed at their ends to receive clamping bells, a lifting device by means of which one centering spindle shaft can be axially advanced relative to the other centering spindle shaft for aligning the lens between the clamping bells along the centering axis, a clamping device for applying a clamping force to a centering spindle shaft that clamps the aligned lens, and at least one machining unit movable relative to the centering axis and having a tool for edge machining of the clamped lens. To enable an optimized bell clamping process, the lifting device and a rotary drive for the axially adjustable centering spindle shaft are arranged coaxially with respect to the centering axis. LIST OF REFERENCE SYMBOLS

[0064] 10Centering machine 12Machine bed 14Holding space 16Lower centering spindle assembly 18Gantry 20Upper centering spindle assembly 22Lower centering spindle 24Lower centering spindle shaft 26Lower centering spindle housing 28Rear housing 30Upper centering spindle 32Upper centering spindle housing 34Upper centering spindle shaft 35Bearing ring 36Clamping bell 38Clamping bell 40Hydraulic expansion chuck 42Hydraulic expansion chuck 44Lifting device 46Measuring system 48Rotary drive 50Clamping and weight compensation device 52Air bearing arrangement 54Lower air bearing section 56Upper air bearing section 58Machining unit 60Machining unit 62Working space 64, 64'X-slide 66, 66'Z-slide 68Guide rail 70Guide rail 72, 72'Guide carriage 74End stop 76Linear motor 78Stator 80Runner 82, 82'Bracket 84, 84'Guide carriage 86, 86'Guide rail 88, 88'Servo motor 90, 90'Headstock 92, 92'Grinding spindle 94, 94'Grinding spindle housing 96Splash guard 98Cooling lubricant supply device 100Face runout measuring device102Moving coil drive 104Coil 106Permanent magnet 108Rotor part 110Screw connection 112Moving coil drive housing 114Housing cover 116Flange plate 118Drive holder 120Upper ring disk 122Lower ring disk 124Web 126Web 128Axial measuring head 130Measuring tape 132Angle measuring head 134Measuring ring 136Measuring head adapter 138Measuring head carrier 140Measuring ring carrier 142Upper shoulder 144Axial / radial air bearing arrangement 145Bearing ring 146Axial bearing pad 148Radial bearing bush 150Anti-rotation device 152Bearing flange 154Stator 156Rotor 158Rotor sleeve 160 Magnet 162 Bearing sleeve 164 Annular piston 165 Cylinder wall 166 Effective surface 168 Annular chamber 170 Effective surface 172 Annular chamber 174 Connecting ring 176 Through hole 178 Feed shoe 180 Seat surface 182 Recess 184 Spring mechanism 186 Extension 188 Bracket 190 Through hole 192 Control spool 194 L-shaped push-in fitting 196 Cross hole 198 Hanger 200 Shoe holder 202 Connecting hole 204 Connecting hole 206 Connecting hole 208 Connecting hole 210 O-ring 212 O-ring 214 O-ring 216 O-ring218 Control spool opening 220 Handle 222 Ball head 224 Mounting 226 Adjusting screw 228 Latch 230 Handle 232 Stop pin 234 Through hole 236 Lip ring 238 Threaded sleeve 240 Helical compression spring 242 Retaining ring 244 External thread 246 Nut 248 Adjusting wheel 250 Button 252 Pneumatic cylinder 254 Piston rod 256 Bracket C1, C2Workpiece rotation axis (angle position controlled) CCentering axis DDirection of rotation of the grinding wheel GTool / grinding wheel LWorkpiece / optical lens QCompressed air source REnd face edge area on the workpiece SCurrent regulator UCircumferential surface of the grinding wheel V1, V2Servo pressure control valve WLinear axis of the clamping bell (position controlled) X1, X2Linear axis of the tool (position controlled) Z1, Z2Linear axis of the tool (position controlled)

Claims

1. Centering machine (10) for workpieces (L), namely optical lenses with curved optical surfaces, with two centering spindles (22, 30), the centering spindle shafts (24, 34) of which, each driven in rotation and accommodated in centering spindle housings (26, 32), are axially aligned with respect to a centering axis (C) and each accommodate a cup-shaped clamping bell (36, 38) at mutually facing ends, a stroke device (44), by means of which one (34) of the centering spindle shafts (24, 34) can be adjusted axially in a sensitive manner along the centering axis (C) with respect to the other (24) of the centering spindle shafts (24, 34) in order to align one of the workpieces (L) between the clamping bells (36, 38) in a bell clamping process, in which the clamping bells (36, 38) are applied to the workpiece (L) with slight pressure in a probing phase before the workpiece (L) is automatically displaced in a direction transverse to the centering axis (C) in an alignment phase as a result of the curvature of its optical surfaces until it has assumed a position between the clamping bells (36, 38) which permits the minimum distance between the clamping bells (36, 38) under the given geometric conditions, a clamping device (50) for applying a clamping force to one (34) of the centering spindle shafts (24, 34) in order to clamp the workpiece (L) aligned between the clamping bells (36, 38) in a clamping phase following the alignment phase, and at least one processing unit (58, 60) movable relative to the centering axis (C) with a tool (G) for edge processing of the workpiece (L) clamped between the clamping bells (36, 38), characterized in that the centering spindle shaft (34) axially adjustable by way of the stroke device (44) is rotationally drivable by means of a rotary drive (48) arranged as the stroke device (44) to be coaxial with respect to the centering axis (C), so that due to the arrangement, which is centered with respect to the centering axis (C), of the rotary drive (48) merely a torque about the centering axis (C) can be generated, without application of a transverse force to the centering spindle shaft (34).

2. Centering machine (10) according to claim 1, wherein the stroke device (44) and the clamping device (50) are arranged coaxially with respect to the centering axis (C).

3. Centering machine (10) according to claim 1 or 2, wherein the stroke device (44) comprises a plunger coil drive (102) which is operatively connected with the axially adjustable centering spindle shaft (34) and which comprises at least one coil (104) coaxial with respect to the centering axis (C) and at least one permanent magnet (106) co-operating with the coil (104).

4. Centering machine (10) according to claim 3, wherein the permanent magnet (106) is secured to a rotor part (108) connected with the axially adjustable centering spindle shaft (34), whereas the coil (104) surrounding the permanent magnet (106) is mounted in a plunger coil drive housing (112) in stationary position in the machine.

5. Centering machine (10) according to any one of the preceding claims, wherein the clamping device (50) comprises an annular piston (164), which is mounted on the axially adjustable centering spindle shaft (34) and on the side thereof remote from the clamping bell end of the axially adjustable centering spindle shaft (34) defines an annular effective surface (166) which bounds in the centering spindle housing (32) an annular chamber (168) by way of which the annular piston (164) can be acted on pneumatically so as to generate the clamping force.

6. Centering machine (10) according to claim 5, wherein the centering spindle (30) with the axially adjustable centering spindle shaft (34) is arranged above the other centering spindle (22), and wherein the annular piston (164) defines on the side thereof facing the clamping bell end of the axially adjustable centering spindle shaft (34) a further annular effective surface (170) which bounds in the centering spindle housing (32) a further annular chamber (172) by way of which the annular piston (164) can be acted on pneumatically in order to ensure pneumatic counterbalancing at the axially adjustable centering spindle shaft (34).

7. Centering machine (10) according to claim 5 or 6, wherein the annular piston (164) is constructed to be unsealed.

8. Centering machine (10) according to any one of the preceding claims, wherein the rotary drive (48) is constructed as an internal rotor torque motor with a stator (154) mounted in the centering spindle housing (32) and a rotor (156) constantly surrounded by the stator (154) and secured to the outer circumference of the axially adjustable centering spindle shaft (34), the rotor being longer than the stator (154) and axially displaceable together with the axially adjustable centering spindle shaft (34) relative to the stator (154).

9. Centering machine (10) according to any one of the preceding claims, wherein the axially adjustable centering spindle shaft (34) is axially displaceable and rotatably mounted in the centering spindle housing (32) by means of an air bearing arrangement (52).

10. Centering machine (10) according to claim 9, wherein the air bearing arrangement (52) has at least two air bearing sections (54, 56), and wherein the rotary drive (48) is arranged axially between the air bearing sections (54, 56).

11. Centering machine (10) according to any one of the preceding claims, further comprising an axial run-out measuring device (100) for checking the centering, by means of which the axial position of an end face edge region (R) of the workpiece (L) clamped between clamping bells (36, 38) is detectable in a direction parallel to the centering axis (C).

12. Centering machine (10) according to claim 11, wherein the axial run-out measuring device (100) comprises a contact caliper (250) which, for positioning with respect to the end face edge region (R) to be scanned at the workpiece (L), is movable together with the processing unit (60).

13. Centering machine (10) according to claim 12, wherein the caliper (250) of the axial run-out measuring device (100) is movable relative to the processing unit (60) from a protected park position behind the workpiece (G) to a measuring position protruding relative to the workpiece (G) and conversely.