Patent Publication Number: US-9844815-B2

Title: Simultaneous turning device for fabrication of eyeglass lenses

Description:
The invention concerns a turning device for the production of eyeglass lenses from lens blanks according to the preamble of Claim  1 , a fabrication mechanism with such a turning device according to Claim  10  and a method for operating the turning device according to Claim  11 . 
     In the prior art lens blanks are used for the production of eyeglass lenses, especially lens blanks of plastic such as polycarbonate, CR39 and so-called “High Index” materials. For reasons of efficiency, the lens blanks are machined in two stages to produce an individual surface, e.g., to produce eyeglass lenses by prescription, namely, first with a milling tool and then with a turning tool. There are combination milling and turning tools [EP 1 291 106 A] and machines with separate milling and (linear or rotational) turning units. In the latter, the eyeglass lenses are machined either in series [EP 1 719 585 A]—the same eyeglass lens is first milled and then turned in the work space of the machine—or in parallel [EP 1 719 582 A1]—different eyeglass lenses are machined at the same time in the work space of the machine, one being milled while the other is turned. 
     Thus, for example, a fabrication mechanism is known from DE 20 2006 021 076 U1, in which a machine on a machine frame has a work piece holder on a carriage, a milling tool and two turning tools. The work piece holder holds a lens blank indirectly across a block piece. However, a direct holding without block piece is also conceivable. The work piece holder at first is moved with the carriage into a working region of the milling tool and the lens blank is milled. Next, the work piece holder is moved into a working region of the first turning tool and the lens blank undergoes lathe machining. After this, the work piece holder is moved into a working region of the second turning tool and the lens blank undergoes another lathe machining. In this way, a spherical, aspherical, toroidal, atoroidal, progressive or free-form geometry can be produced. As a rule, the machining is followed by a fine grinding or polishing process to achieve the necessary surface texture. If need be, coating and/or hardening steps may also follow. 
     The drawback to a device according to DE 20 2006 021 076 U1 is that only a few lens blanks can be machined per unit of time. Thus, the production costs per machined lens blank are high. 
     The device of EP 1 719 582 A1 differs from DE 20 2006 021 076 U1, among other things, in that the turning unit has a work piece spindle and the milling unit has a separate work piece holder. In this way, two lens blanks can be machined at the same time, namely, one with the milling tool and one with the turning tool. By means of a loading mechanism, the milled lens blank is removed from the work piece holder and then placed directly in the work piece spindle, while at the same time a new lens blank is placed in the work piece holder. 
     This boosts the efficiency of the fabrication mechanism and lowers the production costs per machined lens blank as compared to DE 20 2006 021 076 U1. However, the efficiency is still not very high and the production costs per machined lens blank are high. Furthermore, vibrations are transferred from the milling unit to the turning unit, so that the precision of the turning process is low. Vibrations give rise to fabrication inaccuracies and high noise levels. 
     The problem which the invention addresses is to eliminate the drawbacks of the prior art, and to provide a device as well as a method with which a high-quality machining of the lens blanks, a boosting of efficiency, and a lowering of production costs per machined lens blank can be achieved. The invention should be reliable, simple to operate, low in vibration and noise, and cost favourable. 
     The main features of the invention are indicated in the characterizing passage of Claim  1 , in Claim  10  and in Claim  11 . Embodiments are the subject matter of Claims  2  to  9  and  12  to  16 . 
     The invention concerns a turning device having a first turning station with a rotatable first work piece spindle to hold a lens blank and a first turning tool for the machining of a lens blank wherein at least one second turning station with a rotatable second work piece spindle is provided to hold a second lens blank and a second turning tool for the machining of a second lens blank. 
     The advantage of the turning device according to the invention is that the at least two turning stations can simultaneously machine at least two lens blanks. For this, it should be possible to operate the turning stations simultaneously. This results in an especially high efficiency of the turning device and low production costs per machined lens blank, because an upstream milling process per lens blank, which naturally has more coarse manufacturing tolerances, generally takes less time than the turning process, which produces a highly precise surface. Typically, the milling process is around 40% and the turning process around 60% of the total machining time. Thanks to the two turning stations, the cycle times of the milling device and the turning device are well coordinated with each other. Since the milling tool according to the invention typically does not have to wait for the turning tool, the throughput of machinable lenses per unit of time increases substantially. This requires hardly more room for the turning device and the turning device can be combined with a plurality of milling devices, especially without having to split up the manufacturing chain of a milling tool into two lathes, for example. The turning device preferably has a CNC control system, for automated operation if possible. 
     In one variant configuration of the turning device it has a loading device, which is configured to load lens blanks into the work piece spindles. Thus, the loading is automated and can be easily carried out. Preferably, the loading device also unloads the work piece spindles. 
     In a special variant of the loading device, a pair of holding means is provided for each turning station to hold two lens blanks, the holding means of the pairs being oriented at an angle to each other and interconnected, and the pairs of holding means being able to rotate about a common turning axis. This enables a very fast replacement of lens blanks in the work piece spindles. Thus, the efficiency of the turning device is especially high. Such pairs of holding means or the turning axis can be mounted on a transport arm, especially for a parallel displacement of the turning axis. For the angled connection of the pairs, a right-angled arrangement of the two holding means  34  works well. Preferably, the turning axis is oriented perpendicular to the spindle axes of the work piece spindles. Moreover, the spacing between the pairs of holding means preferably corresponds to the spacing between the spindle axes. Thus, only a few movement sequences need to be carried out for a lens blank replacement and correspondingly few actuators are needed. 
     Furthermore one variant of the invention has the work piece spindles with parallel oriented spindle axes. This enables a compact configuration of the turning device and the work piece spindles and the loading device have an uncomplicated motion kinematics. In particular, the work piece spindles can share actuators/drive units. For the same reasons, the work piece spindles are preferably arranged in a common spindle plane. 
     Furthermore, the option exists that the turning stations, preferably the work piece spindles, have a common transverse drive, with which the spacing of the turning tools relative to the spindle axis of a coordinated work piece spindle can be changed, in particular, transversely to the spindle axis or by a displacement in the spindle plane. Thus, the turning stations can be arranged alongside each other in space-saving manner, since no collisions are possible, especially if the turning tools are arranged on a common transverse carriage. Furthermore, a common transverse drive can be cheaply realized. Optionally, the work piece spindles can travel out from the working region of the turning tools for the lens blank replacement. Moreover, the turning tools are preferably oriented parallel to each other. Furthermore, the turning tools should be arranged in a common tool plane. Alternatively or additionally, the turning tools can also have a common second transverse drive, especially when the turning tools are arranged on a common second transverse carriage. 
     In one special embodiment, the turning stations have a common machine frame and/or a common machine bed. According to another preferred embodiment, the turning tools lie in a common work space. Both solutions contribute to a compact configuration and all parts of the turning device are positioned precisely to one another. Safety mechanisms can also be easily provided. 
     Another configuration option is for the turning stations, preferably the work piece spindles, to have a common linear drive with which the spacing of the turning tools relative to a coordinated work piece spindle can be changed, especially in the axial direction of the spindle axes or by a parallel displacement of the spindle plane. Thus, only one linear drive is needed, especially if the work piece spindles are mounted on a common longitudinal carriage. This is economical. Alternatively or additionally, the turning tools can also have a common second linear drive, especially when the turning tools are arranged on a common second longitudinal carriage. 
     The longitudinal carriages and the transverse carriages can be configured here as a cross table arrangement. The optional second longitudinal carriage and second transverse carriage can also be configured as a second cross table arrangement. 
     Alternatively, the work piece spindles and/or the turning tools can also have independent linear and/or transverse drives. This would achieve an especially high flexibility, whereby two greatly differing surface topographies could be machined at the same time. 
     Furthermore, a special configuration of the turning device has each turning tool with its own fast tool servomotor, by which the infeed depth can be changed with respect to a coordinated work piece spindle. Thus, the turning tools can be fed in independently of each other and in this way produce different surface topographies on the lens blanks. 
     Preferably, the linear drive has a maximum first travel and the fast tool servomotors a maximum second travel, while the maximum first travel corresponds to at least 10 times the maximum second travel. This makes it possible to produce with the large first travel of the linear drive a coarse and essentially rotationally symmetrical surface topography, especially on each lens blank in the turning device. At the same time, the fast tool servomotors with the small second travel take care of the individualization of the surface topography. It is possible here to produce non-rotationally symmetrical surface topographies, which can also be configured different between the turning stations. Especially suitable is a particular configuration of the turning device in which the fast tool servomotor has a piezo-drive. Piezo-drives are especially fast and precise. 
     Moreover, an optional configuration is provided in which the turning device has a control electronics to put out drive signals to the work piece spindles, the transverse drive, the linear drive and the fast tool servomotors, wherein the drive signals of the control electronics are matched up with each other. In this way, even in the case of common transverse and linear drives it is possible to produce the desired surface topographies. Accordingly, the drive signals of the control electronics should be matched up with each other for the simultaneous making of different surface topographies on the lens blanks. 
     For vibration optimization, it is favourable for the drive signals from the control electronics to be attuned to each other such that the fast tool servomotors are driven oppositely at least temporarily or in phases by the drive signals for the fast tool servomotors for vibration dampening. The accelerated masses thus oscillate oppositely at least partly and neutralize each other. This results in more precisely fabricated surfaces on the lens blank and reduces the wear to the turning device. In addition, the noise levels are much lower and so a high machine quality rating is observable and less strict health and safety measures with regard to hearing protection are necessary. 
     The invention furthermore concerns a fabrication mechanism for the manufacturing of eyeglass lenses from lens blanks, with a milling device and with a turning device as described above. The milling device has at least one milling station with a work piece holder to hold a lens blank and a milling tool for machining the lens blank. Moreover, a loading device is provided, which is configured to remove lens blanks from the milling device and load them into the work piece spindles, preferably in fully automated manner. 
     The advantage of the fabrication mechanism according to the invention is that thanks to the at least two turning stations provided and the independence of the work piece holders from the work piece spindles at least two lens blanks can be machined by turning and milling at the same time. This results in an especially high efficiency of the fabrication mechanism and low production costs per machined lens blank. Since the milling tool of the invention typically needs little or no waiting for the turning tool, the throughput of machined lenses per unit of time rises substantially. The fabrication mechanism preferably has a common CNC control system. 
     The milling device is preferably suitable not only for the machining of the lens surface but also for machining the lens circumference. For this, there can be provided a surface milling cutter, especially a ball-head milling cutter, for the surface machining, and an edge milling cutter, especially an end mill, for the circumference machining. Preferably the two can be or are driven independently and simultaneously. 
     In a more specific embodiment of the fabrication mechanism the turning device has 1.5 times to 2.5 times as many turning stations as the milling device has milling stations. In this way, the machining speed of the turning device and the milling device can be attuned to each other so that only very slight waiting times exist for the milling device and the turning device. 
     According to a special variant of the fabrication mechanism the milling device has precisely one milling station and the turning device precisely two turning stations. This accomplishes a high efficiency with reasonable production costs for the fabrication mechanism. 
     Basically the turning device and the milling device can be independent machines which are arranged along a manufacturing line in different positions. In this way, existing turning and/or milling devices can be combined with each other. 
     For a compact configuration of the fabrication mechanism and a precise relative arrangement with respect to each other, a configuration is advisable in which the milling device and the turning device have a common machine frame and/or a common machine bed. A common machine bed costs little, it can be monolithic in configuration, and all machine parts are positioned correctly relative to each other. According to one special embodiment, the milling device, the turning device and the loading device have a common machine frame and/or a common machine bed. In this way, the loading device is also positioned precisely relative to the turning and the milling device. 
     In a modified variant, the milling device and the turning device are vibration-decoupled, preferably by foundations separated by the floor. Thus, no vibrations can be transmitted from the milling device to the turning device and the precision of the turned surface is high. Separate machine beds of the milling and the turning device also contribute to this. Furthermore, transport is easier on account of the lower individual weights. Separate machine beds can be positioned relative to each other through an optional common machine frame. Preferably, however, the floor forms the only mechanical connection between the milling device and the turning device. The loading device is preferably separated at least mechanically from the milling device or at least mechanically from the milling device. A mechanical connection of the loading device to the floor can be provided each time. 
     The fabrication mechanism can be provided cheaply if the milling device and the turning device are arranged in a common manufacturing cell. Preferably, the loading device is also arranged in the manufacturing cell. The manufacturing cell should have a housing shell, inside which the turning device and the loading device are arranged. Work safety devices such as entrance barriers then only need to be provided once for both devices. Preferably, the manufacturing cell is vibration-decoupled from the turning device and/or the milling device. 
     For the protection of the high precision turning device it is advisable to expand the fabrication mechanism such that the milling device and the turning device are arranged in separate work spaces, while the work spaces are preferably separated from each other at least in regard to transfer of machining chips. This is accomplished either by sufficient distance between the milling device and the turning device or by mechanical separation means such as chip shields, flaps or housing each time between the milling device and the turning device. 
     According to a more specific configuration of the loading device, this has a transport means for the transport of a lens blank from the milling station to the turning stations. Preferably, the transport means is movable between the work piece holders and the work piece spindles. For short distances and a precise positioning, transport arms with grips or suction cups are suitable. Longer distances can be spanned with slides, conveyor belts, or conveyor rails. At their ends another transport arm can be provided for passing the lens blanks to or from the work piece spindles and/or work piece holders. 
     In order to remove a lens blank from the work piece holder even when lens blanks are being held in the work piece spindles, the loading device should have a lens magazine for at least one lens blank, preferably for at least two lens blanks. In particular, the loading device should be able to hold as many lens blanks as the turning device has turning stations. In this way, at least as many premilled lens blanks can be kept on hand as can be placed in the work piece spindles. Especially preferably, the loading device has a lens magazine for at least twice as many lens blanks as the turning device has turning stations. In this way, the loading device, preferably a transport arm, can hold at the same time two new lens blanks and two lathe machined lens blanks. This enables an especially fast changing of lens blanks. 
     Furthermore, the invention concerns a method for the operation of an above-described turning device, in which a first and a second lens blank are loaded into the work piece spindles, this being followed by simultaneous machining of the first and the second lens blank with the turning tools, wherein the control electronics attunes the drive signals to each other such that the drive signals for the fast tool servomotors accomplish at least a temporary or phase-wise opposite running of the fast tool servomotors for vibration dampening. The accelerated masses thus oscillate oppositely at least partly, in particular at individual amplitudes, and neutralize each other. This results in more precisely fabricated surfaces on the lens blank and reduces the wear to the turning device. In addition, the noise levels are much lower and so a high machine quality rating is identifiable and less strict health and safety measures with regard to hearing protection are necessary. 
     According to one preferred embodiment of the method, different surface topographies are produced on the lens blanks simultaneously in the turning stations. This makes allowance for the usually necessary individual correction for visual defects of an eye. 
     In a special embodiment of the method, the drive signals for the fast tool servomotors accomplish an opposite running of the fast tool servomotors at least at one of the 20% largest set point gradients for each revolution of the lens blanks. Thus, the number of large accelerations acting in the same direction is reduced. 
     In a more specific embodiment of the method, the control electronics attunes the rhythm of the fast tool servomotors to each other by modulating the rotational speeds of the work piece spindles. In this way, the opposite acceleration energies of the first and second fast tool servomotors can be clocked. 
     Preferably, the method is expanded in that the control electronics carries out a vibration simulation before each machining of the lens blanks. Thus, less computing power is required during the turning process, because a real-time calculation is not necessary. However, the actual vibrations can also optionally be sensed by way of acceleration sensors and the drive signals attuned in real time, in order to optimize the vibrations. The data of the real-time attuning can be used to optimize the future vibration simulations. It is appropriate to use the vibration simulation to decide whether the work piece spindles are driven oppositely or concurrently. The direction of rotation with the better optimization possibility is then selected. 
     According to a special variant of the method, the control electronics optimizes or minimizes the sum of the positive and negative acceleration energies of the first and the second fast tool servomotor and/or keeps the sum of the acceleration energies below a defined value. The former is intended to ensure that as much neutralization of the vibrations as possible takes place in total. When the acceleration energies are kept below a defined value, fewer load peaks and noise spikes occur. 
     Furthermore, the invention concerns a method for the operation of a fabrication mechanism as described above, in which the following steps are carried out:
         a) loading of a first lens blank into the work piece holder and machining of the first lens blank with the milling tool;   b) removal of the first lens blank from the work piece holder with the loading device;   c) subsequent loading of a second lens blank into the work piece holder and machining of the second lens blank with the milling tool;   d) subsequent removal of the second lens blank from the work piece holder with the loading device;   e) loading of the first and second lens blank into the work piece spindles with the loading device, preferably at the same time, and loading of a third lens blank into the work piece holder;   f) Simultaneous machining of the third lens blank with the milling tool and of the first and second lens blank with the turning tools.       

     It will be recognized that with this method two lens blanks are machined by turning and one lens blank by milling in a particular time slot. The numbering of the lens blanks has nothing to do with the working off of the sequence of the method. It is only important that two lens blanks are machined by turning while a third lens blank is machined by milling. Therefore, for example, it does not matter if the loading device has a lens magazine for several lens blanks and other lens blanks are machined between the first, second and third lens blank. 
     It is advantageous for the method that an especially high efficiency of the fabrication mechanism and low production costs per machined lens blank are achieved. Thanks to the number of turning stations per milling station the waiting times of the milling and or the turning tools can be reduced. In this way, the throughput of machined lenses per unit of time is high. Preferably, with the milling process one leaves an allowance for the turning process of 0.2 mm to 0.3 mm as compared to the desired surface topography. It is essentially possible to create a rotationally symmetrical surface with the milling tool, or to create already a non-rotationally symmetrical surface topography. In the latter case, the milling device already produces a free-form surface if such a one is to be lathe machined afterwards. 
     Preferably the circumferential geometry of the lens blank is also machined with the milling tool. In this way, already at this point in time a circumferential geometry adapted to an eyeglass lens frame can be produced. To avoid breakage on the lens margin during later entry and exit of the turning tool, a bevel should be produced with the milling tool at the circumference of the lens blank. 
     According to a more specific layout of the method, step g) is provided, in that there is a removal of the third lens blank from the work piece holder with the loading device and a loading of a fourth lens blank into the work piece holder and a machining of the fourth lens blank with the milling tool (all) during the machining of the first and the second lens blank with the turning tools. This ensures that the milling tool does not have to wait for the turning tool, which in a typical application takes longer for each lens blank than the milling tool. 
     The method can be optionally continued with the following steps:
         h) removal of the first and the second lens blank from the work piece spindles;   i) subsequent loading of one or the third and one or the fourth lens blank into the work piece spindles with the loading device and loading of a fifth lens blank into the work piece holder;   j) repeating of steps f) through i).       

     With this an endless loop is achieved, resulting in a high throughput of machined lens blanks. The repeating of steps f) through i) is done with adapted numbering of the lens blanks. 
     In a special variant of the method, the turning stations have a common transverse drive, with which the spacing of the turning tools relative to the spindle axis of a coordinated work piece spindle can be changed, and the turning stations have a common linear drive, with which the spacing of the turning tools relative to a coordinated work piece spindle can be changed, where each turning tool has its own fast tool servomotor, with which the infeed depth can be changed with regard to a coordinated work piece spindle, while the turning device has a control electronics for putting out drive signals to the work piece spindles, the transverse drive, the linear drive and the fast tool servomotors, and the drive signals of the control electronics are attuned to each other, and where the control electronics attunes the drive signals to each other such that the drive signals for the fast tool servomotors accomplish at least a temporary opposite running of the fast tool servomotors for vibration dampening. 
     In this way, the vibrations can be specifically cancelled out or mitigated by the fast-acting fast tool servomotors. This is accomplished, for example, in that the drive signals for the fast tool servomotors bring about an opposite running of the fast tool servomotors at least on a large set point gradient of the infeed depth as compared to the rest of the surface topography. By a large set point gradient is meant 20% of the largest set point gradient of a surface topography being produced for each revolution of the work piece spindle. In particular, the rhythm of the fast tool servomotors can be attuned to each other by modulating the rotational speeds of the work piece spindles. 
     According to the method, the control electronics for the purpose of vibration dampening should put out drive signals to the work piece spindles which bring about an opposite running or a concurrent running of the work piece spindles. A decision making logic for the direction and speed of rotation of the work piece spindles is provided with the aid of a vibration simulation. 
     Insofar as individual surface topographies are to be produced on all lens blanks, the attuning of the drive signals is done for each pair of lens blanks being machined. Preferably, the attuning is at least partly established already prior to the loading of the pair of lens blanks into the work piece spindles. 
     The above-described method for the operation of the turning device can be integrated into the method for the operation of the fabrication mechanism. 
    
    
     
       Further features, details and benefits of the invention will emerge from the wording of the claims and from the following description of sample embodiments with the aid of the drawings. There are shown: 
         FIG. 1  a perspective view of a turning device; 
         FIG. 2  a perspective view of a turning device with housing removed; 
         FIG. 3  a side view of a turning device; 
         FIG. 4  a side view of a turning device with housing removed; and 
         FIG. 5  a diagram of a fabrication mechanism with a turning device and a milling device; 
         FIG. 6  a diagram showing the accelerations of two fast tool servomotors in synchronous operation and the sum thereof over time; 
         FIG. 7  a diagram showing the accelerations of two fast tool servomotors in phase-shifted asynchronous operation and the sum thereof; and 
         FIG. 8  a diagram showing actual measurement results of the accelerations of two fast tool servomotors in vibration-optimized asynchronous operation and the sum thereof over time for a simultaneous turning cycle of two lens blanks. 
     
    
    
       FIGS. 1, 2, 3 and 4  show from various perspective views a turning device  50 , which has two turning stations  51   a ,  51   b . Not all technical features and thus not all reference numbers are visible in each of  FIGS. 1 to 4 . The first turning station  51   a  has a rotatable first work piece spindle  52   a  to hold a first lens blank  100   a  and a first turning tool  53   a  for the machining of the lens blank  100   a  so held. At the same time, the second turning station  52   b  has a rotatable second work piece spindle  52   b  to hold a second lens blank  100   b  and a second turning tool  53   b  for the machining of the second lens blank  100   b  so held. The first and the second work piece spindles  52   a ,  52   b  have parallel oriented spindle axes A 1 , A 2 . Furthermore, the first and the second work piece spindle  52   a ,  52   b  are arranged in a common spindle plane E 1 . The turning stations  51   a ,  51   b  are of the same type and are designed for machining of lens blanks  100   a ,  100   b  of the same type. In particular, the work piece spindles  51   a ,  51   b  are (for the most part) identical in design and the turning tools  53   a ,  53   b  are (for the most part) identical in design. 
     The first and second work piece spindle  52   a ,  52   b  of the two turning stations  51   a ,  51   b  are mounted on a common machine bed  70 , which is monolithic in design. Furthermore, the two turning stations  51   a ,  51   b  have a common transverse drive  73 , with which the spacing X 1  of the turning tools  53   a ,  53   b  relative or transverse to the spindle axis A 1 , A 2  of a coordinated work piece spindle  52   a ,  52   b , respectively, can be changed. For this, the first and the second work piece spindle  52   a ,  52   b  are mounted on a common transverse carriage. In this way, the work piece spindles  52   a ,  52   b  can also be driven out to the side from the work space of the turning tools  53   a ,  53   b  for a blank change, as shown in  FIG. 2 . 
     In addition, the turning stations  51   a ,  51   b , especially the work piece spindles  52   a ,  52   b , have a common linear drive  74 , with which the spacing X 2  of the turning tools  53   a ,  53   b  relative to a coordinated work piece spindle  52   a ,  52   b  can be changed, especially in the axial direction of the spindle axes A 1 , A 2 . For this, the two work piece spindles  52   a ,  52   b  are mounted on a common longitudinal carriage. The longitudinal carriage, in turn, is mounted on the transverse carriage, which in turn is mounted on the machine bed  70 . In this way, there is a cross table arrangement on the machine bed  70 . 
     Optionally, the work piece spindles  52   a ,  52   b  and/or the turning tools  53   a ,  53   b  can also have independent linear and/or transverse drives  73 ,  74 . If independent linear and transverse drives  73 ,  74  are provided, there will be two independent cross table arrangements. An especially high flexibility would be achieved, and at the same time two greatly differing surface topographies could be machined. 
     Both turning tools  53   a ,  53   b  have their own fast tool servomotor  75   a ,  75   b  with piezo-drive, with which the infeed depth T can be changed in relation to a coordinated work piece spindle  52   a,    52   b . The fast tool servomotors  75   a ,  75   b  are firmly connected to the machine bed  70 . The turning tools  53   a ,  53   b , especially lathe cutters or cutting inserts, are also oriented parallel to each other and arranged in a common tool plane E 2 . The maximum travel of the linear drive  74  is at least 10 times larger than the maximum travel of the fast tool servomotors  75   a ,  75   b  and the lathe cutters/cutting inserts driven by them. 
     Both turning stations  51   a ,  51   b  can be driven at the same time. With the cross carriages, two lens blanks  100   a ,  100   b  can be positioned at the same time rotating in front of the turning tools  53   a ,  53   b . Since the turning device  50  has a control electronics  54  for putting out drive signals S 1   a , S 1   b , S 2 , S 3 , S 4   a , S 4   b  to the work piece spindles  52   a ,  52   b , the transverse drive  73 , the linear drive  74  and the fast tool servomotors  75   a ,  75   b  (see  FIG. 1 ), and the drive signals S 1   a , S 1   b , S 2 , S 3 , S 4   a , S 4   b  of the control electronics  54  are matched up with each other, different surface topographies can be produced on the two lens blanks  100   a ,  100   b  at the same time. 
     Furthermore, a loading device  30  is provided, which is designed to load lens blanks  100   a ,  100   b ,  100   d ,  100   e  into the work piece spindles  52   a ,  52   b . For this, the loading device  30  has transport means  31  and a lens magazine  32 . The transport means  31  include a conveyor rail  33  and holding means  34  on a transport arm  35 . The holding means  34  have suction cups. The optional and special configuration of the loading device  30  calls for four holding means  34  to be mounted on the transport arm  35 . Every two of the four holding means  34  are joined together at an angle, here in particular, a right angle. The two pairs of holding means  34  are able to turn about a common turning axis. The turning axis is oriented perpendicular to the spindle axes A 1 , A 2 . Furthermore, the distance between the pairs of holding means  34  corresponds to the distance between the spindle axes A 1 , A 2 . On the conveyor rail  33  there are arranged carriages/carts, with which large distances can be covered. The carriages/carts together with the holding means  34  form the lens magazine  32 . 
     With this arrangement of the loading device  30  it is possible to take up two previously milled lens blanks at the same time, in particular one lens blank per pair of the holding means  34 . With the two free holding means  34  it is then possible to remove two lens blanks  100   a ,  100   b  from the work piece spindles  52   a ,  52   b . After a rotation of the pairs of holding means by 90 degrees, the lens blanks previously taken up can be loaded into the work piece spindles  52   a ,  52   b . The already machined lens blanks  100   a ,  100   b  are then set down on the free carriages/carts. Two new premilled lens blanks are then provided with a new carriage/cart and can be picked up by the holding means  34 . The loading and unloading of the work piece spindles  52   a ,  52   b  is thus especially fast and the efficiency of the turning device  50  is high. Of course, the angle of rotation of the pairs of holding means depends on the angle between their legs and need not be exactly 90 degrees. 
     With the conveyor rail  33  the turning device  50  can be easily linked to other machines, such as milling devices and/or coating devices. The loading device  30  or parts thereof should be connected to the machine bed  70 . In particular, the transport arm  35  should have a firm connection with the machine bed  70 . In this way, it is oriented exactly with respect to the work piece spindles  52   a ,  52   b . The conveyor rail is preferably vibration-decoupled from the machine bed  70  or an additional machine frame. 
     As can be seen in  FIGS. 1 and 3 , the two turning stations  51   a ,  51   b  of the turning device  50  are arranged in a common manufacturing cell  71 . The manufacturing cell  71  is formed by a housing shell  72 . Between the turning stations  51   a ,  51   b  there is only a gap, but no mechanical elements. Chip shields or the like can be provided optionally. The transport arm  35  connects the conveyor rail  33  outside the manufacturing cell  71  to the work piece spindles  52   a ,  52   b  arranged inside the manufacturing cell  71 . In this way, the turning device  50  can be combined with a milling device, while the turning stations  51   a ,  51   b  are arranged in a work space which is independent of the milling tool. Therefore, a chip transfer between the turning and the milling device is prevented. 
     A fabrication mechanism  1  for the manufacture of eyeglass lenses from lens blanks  100   a ,  100   b ,  100   c ,  100   d ,  100   e , with a milling device  10  and a turning device  50 , is shown in the diagram of  FIG. 5 . 
     Of the turning device  50 , one notices in particular two turning stations  51   a ,  51   b . The two turning stations  51   a ,  51   b  each have a rotatable work piece spindle  52   a  to hold a lens blank  100   a ,  100   b ,  100   c ,  100   d ,  100   e  and a turning tool  53   a ,  53   b  for the machining of a lens blank  100   a ,  100   b ,  100   c ,  100   d ,  100   e  so held. 
     The work piece spindles  52   a ,  52   b  have parallel oriented spindle axes A 1 , A 2  and are arranged in a common spindle plane E 1 . By means of a common transverse drive  73  the work piece spindles  52   a ,  52   b  can be moved in the spindle plane E 1  such that the spacing X 1  of the turning tools  53   a ,  53   b  relative to the spindle axis A 1 , A 2  of a coordinated work piece spindle  52   a ,  52   b  can be changed. 
     Furthermore, the work piece spindles  52   a ,  52   b  have a common linear drive  74 , by which the spacing X 2  of the turning tools  53   a ,  53   b  relative to a coordinated work piece spindle  52   a ,  52   b  can be changed, in particular, by a parallel displacement of the spindle plane E 1 . 
     Opposite the work piece spindles  51   a ,  51   b  are firmly mounted the turning tools  53   a ,  53   b . The two lathe cutters of the turning tools  53   a ,  53   b  lie with their cutting edges  55   a ,  55   b  in the plane of the spindle axes A 1 , A 2  of the two work piece spindles  52   a ,  52   b . Furthermore, the distance between the cutting edges  55   a ,  55   b  of the lathe cutters corresponds to the distance between the two spindle axes A 1 , A 2 . One notices that the two turning tools  53   a ,  53   b  are also oriented parallel to each other and are arranged in a common tool plane E 2 , this applies especially to the lathe cutters. Each turning tool  53   a ,  53   b  has its own fast tool servomotor  75   a ,  75   b  with a piezo-drive, by which the infeed depth T of the cutting edges of the lathe cutters  53   a ,  53   b  can be changed relative to a coordinated work piece spindle  52   a ,  52   b . The linear drive  74  has a maximum first travel and the lathe cutters  53   a ,  53   b  a maximum second travel, the maximum first travel being at least 10 times the maximum second travel. 
     In this way, the turning stations  51   a ,  51   b  can be driven simultaneously. Even so, different surface topographies can be machined on the lens blanks  100   a ,  100   b  at the same time. This is especially because of the rapid and independent modulation of the infeed depth T. 
     Furthermore, one sees in  FIG. 5  the milling device  10  with exactly one single milling station  11 . On a work piece holder  12  of the milling station  11 , a third lens blank  100   c  has been taken up. In the present instance, the work piece holder  12  has a spindle drive for rotating the lens blank  100   c  about a turning axis A 3 . The work piece holder  12  is movable in the longitudinal and transverse direction, especially thanks to a cross table arrangement. 
     Opposite the work piece holder  12  is firmly positioned a milling tool  13 . The milling tool  13  has a surface milling cutter  14 , especially with ball-head milling cutter, with a first drive, and an edge milling cutter  15 , especially with end mill, with a second drive. 
     By movements of the work piece holder  12  in the longitudinal and transverse direction as well as rotation of the third lens blank  100   c , the latter will be moved either into the surface milling cutter  14  or into the edge milling cutter  15 . In this way, the surface or the circumference of the third lens blank  100   c  will be machined. 
     The turning device  50  and the milling device  10  are connected via a loading device  30 , which is designed to remove lens blanks  100   a ,  100   b ,  100   c ,  100   d  from the milling device  10  and load them into the work piece spindles  52   a ,  52   b . For this, a movable transport means  31  has several holding means  34 , in particular, two. In this way, the transport means  31  also forms a lens magazine  32 , in which milled lens blanks, here a fourth lens blank  100   d , are kept temporarily prior to being loaded into the work piece spindles  52   a ,  52   b.    
     The turning device  50  and the loading device  30  can optionally be designed as shown in  FIGS. 1 to 4 . 
     Furthermore, the design option exists of mounting the milling device  10 , the turning device  50  and in some cases also the loading device  30  on a common machine frame and/or a common machine bed  70 . A common machine bed  70  would preferably be monolithic in design. However, a mechanical vibration decoupling between the milling device  10  and the turning device  50  is preferable, especially by foundations separated by the floor. 
     When the milling device  10 , the turning device  50  and preferably the loading device  30  are arranged in a common manufacturing cell  71 , safety precautions and housings only need to be provided once. Preferably, the milling device  10  and the turning device  50  furthermore lie in separate work spaces, and the work spaces are preferably separated from each other at least in regard to transfer of machining chips. 
     With such a fabrication mechanism  1 , the methods of the invention can be implemented. In particular, it is possible to load at first a first lens blank  100   a  into the work piece holder  12  and to machine it with the milling tool  13 . Next, the first lens blank  100   a  will be removed with the loading device  30  from the work piece holder  12 , before a second lens blank  100   b  is loaded into the work piece holder  12  and machined with the milling tool  13 . After the second lens blank  100   b  has also removed with the loading device  30  from the work piece holder  12 , the first and second lens blank  100   a ,  100   b  can be loaded with the loading device  30  into the work piece spindles  52   a ,  52   b . Then a simultaneous machining of a third lens blank  100   c  with the milling tool  13  and of the first and second lens blank  100   a ,  100   b  with the turning tools  53   a ,  53   b  is possible. 
     A diagram showing the accelerations B 1 , B 2  of two fast tool servomotors in synchronous operation over time t can be seen in  FIG. 6 . The sum S thereof is the addition of the individual values of the accelerations B 1  and B 2 . The peaks of the sum are located outside the image area. It can be seen that large acceleration forces act in sum S, exciting strong vibrations in an above-described turning device and causing loud noise. 
     Contrary to  FIG. 6 ,  FIG. 7  shows a diagram which is based on the accelerations B 1 , B 2  of two fast tool servomotors in phase-shifted asynchronous operation. The sum S thereof is much lower than the individual accelerations B 1  and B 2 , and so a considerable reduction in vibration can be achieved compared with synchronous operation in  FIG. 6  or with a turning device having only one turning station. This results in little wear, high surface precision on lathe machined lens blanks and quiet operation. 
     In contrast to the idealized asynchronous operation according to  FIG. 7 ,  FIG. 8  shows a diagram showing actual measurement results of the accelerations B 1 , B 2  of two fast tool servomotors in vibration-optimized asynchronous operation and the sum thereof over time. The time span of the illustration extends over a simultaneous turning cycle of two lens blanks. The large acceleration amplitudes B 1 , B 2  of the two fast tool servomotors, which decrease with increasing degree of fabrication of the surface topographies on the two lens blanks, can be seen. In particular, less considerable gradients are present on the surface of the lens blanks in the centre of the lens blank. 
     Along the time axis, the resulting sum of the two accelerations B 1  and B 2  can be seen. This sum is clearly much lower than that of the individual accelerations B 1 , B 2  and also than their values. This results in particularly low vibrations and noise. 
     These improvements are achievable by different measures for optimizing the asynchronous operation. In particular by a method for the operation of a turning device according to  FIGS. 1 to 5 , in which a first and a second lens blank are loaded into the work piece spindles, this being followed by simultaneous machining of the first and the second lens blank with the turning tools, wherein the control electronics attunes the drive signals to each other such that the drive signals for the fast tool servomotors accomplish at least a temporary or phase-wise opposite running of the fast tool servomotors for vibration dampening. The accelerated masses thus oscillate oppositely at least partly, in particular at individual amplitudes, and neutralize each other. This occurs, as also shown in  FIG. 8 , when different surface topographies are produced on the lens blanks simultaneously in the turning stations. 
     Preferably, the drive signals for the fast tool servomotors accomplish an opposite running of the fast tool servomotors at least at one of the 20% largest set point gradients for each revolution of the lens blanks. Thus, the number of large accelerations acting in the same direction is reduced. 
     Furthermore, when the control electronics attunes the rhythm of the fast tool servomotors to each other by modulating the rotational speeds of the work piece spindles, this contributes to the improvements. In this way, the opposite acceleration energies of the first and second fast tool servomotors can be clocked. 
     Preferably, the control electronics already carries out a vibration simulation before the machining of a pair of lens blanks. A high degree of target achievement is achieved when the control electronics optimizes or minimizes the sum of the positive and negative accelerations B 1 , B 2  of the first and the second fast tool servomotor. This means that the area or the integral of the sum S is minimized along the time axis t. In addition, individual extreme amplitudes of the sum S are avoided. This is achieved in that the sum S is kept below a defined value. Even when the integral of the sum S is slightly increased as a result along the time axis t, this elimination of peaks contributes to less wear, better turning surfaces and less noise. 
     Refer to the above general description and the claims for possible implementations of the method. 
     The invention is not limited to the above described embodiments, but rather can be modified in many ways. First and foremost, the features of the turning device, the milling device and the loading device should be considered independently of each other, especially when no (mechanical) interfaces are involved. 
     All features and benefits emerging from the claims, the description, and the drawing, including design details, spatial arrangements, and steps of the method, can be essential to the invention by themselves or in the most diverse of combinations. 
     LIST OF REFERENCE NUMBERS 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                  1 
                 Fabrication mechanism 
               
               
                   
                  10 
                 Milling device 
               
               
                   
                  11 
                 Milling station 
               
               
                   
                  12 
                 Work piece holder 
               
               
                   
                  13 
                 Milling tool 
               
               
                   
                  14 
                 Surface milling cutter 
               
               
                   
                  15 
                 Edge milling cutter 
               
               
                   
                  30 
                 Loading device 
               
               
                   
                  31 
                 Transport means 
               
               
                   
                  32 
                 Lens magazine 
               
               
                   
                  33 
                 Conveyor rail 
               
               
                   
                  34 
                 Holding means 
               
               
                   
                  35 
                 Transport arm 
               
               
                   
                  50 
                 Turning device 
               
               
                   
                  51a 
                 First turning station 
               
               
                   
                  51b 
                 Second turning station 
               
               
                   
                  52a 
                 First work piece spindle 
               
               
                   
                  52b 
                 Second work piece spindle 
               
               
                   
                  53a 
                 First turning tool 
               
               
                   
                  53b 
                 Second turning tool 
               
               
                   
                  54 
                 Control electronics 
               
               
                   
                  70 
                 Machine bed 
               
               
                   
                  71 
                 Manufacturing cell 
               
               
                   
                  72 
                 Housing shell 
               
               
                   
                  73 
                 Transverse drive 
               
               
                   
                  74 
                 Linear drive 
               
               
                   
                  75a 
                 First fast tool servomotor 
               
               
                   
                  75b 
                 Second fast tool servomotor 
               
               
                   
                 100a 
                 First lens blank 
               
               
                   
                 100b 
                 Second lens blank 
               
               
                   
                 100c 
                 Third lens blank 
               
               
                   
                 100d 
                 Fourth lens blank 
               
               
                   
                 100e 
                 Fifth lens blank 
               
               
                   
                 A1 
                 Spindle axis (first work piece spindle) 
               
               
                   
                 A2 
                 Spindle axis (second work piece spindle) 
               
               
                   
                 A3 
                 Turning axis (work piece holder) 
               
               
                   
                 E1 
                 Spindle plane (work piece spindles) 
               
               
                   
                 E2 
                 Tool plane (turning tools) 
               
               
                   
                 S1a 
                 Drive signal (first work piece spindle) 
               
               
                   
                 S1b 
                 Drive signal (second work piece spindle) 
               
               
                   
                 S2 
                 Drive signal (transverse drive) 
               
               
                   
                 S3 
                 Drive signal (linear drive) 
               
               
                   
                 S4a 
                 Drive signal (first fast tool servomotor) 
               
               
                   
                 S4b 
                 Drive signal (second fast tool servomotor) 
               
               
                   
                 T 
                 Infeed depth (fast tool servomotor) 
               
               
                   
                 X1 
                 Spacing (turning tools - spindle axis) 
               
               
                   
                 X2 
                 Spacing (turning tool - work piece spindle)