Abstract:
The invention relates to a machine for processing plastic workpieces. A machine housing surrounds a working chamber located between a workpiece spindle for rotationally driving the workpieces about a workpiece axis of rotation and a fast tool servo for producing an oscillating feeding movement of a rotary tool in the direction of the workpieces. The workpiece spindle is provided with a carriage which can be driven and is guided on at least two guide surfaces of a guiding arrangement in order to produce a relative advancing movement between the workpiece and the rotary tool. The advancing movement runs transversely with respect to the feeding movement and defining therewith a processing plane in which during processing the rotary tool engages with the workpiece. The guiding arrangement is mounted on the machine housing such that the processing plane extends between the two guide surfaces.

Description:
TECHNICAL FIELD 
     The present invention relates generally to a machine for processing optical workpieces. In particular, the invention relates to a machine for processing spectacle lenses of plastics material such as is widely used in so-called “RX workshops”, i.e. production facilities for large-scale production of individual spectacle lenses according to prescription. 
     PRIOR ART 
     For the processing of plastics material spectacle lenses there is usually a spectacle lens blank, also termed “blank”, which is injection-molded from plastics material (for example polycarbonate, CR  39 , HI index, etc.) and which has a standardized finished convex outer surface with, for example, a spherical or progressive shape. The usually concave inner or prescription surfaces receive, by way of a cutting machining, a spherical, aspherical, toroidal, atoroidal, progressive or free-shape geometry (progressive surfaces) depending on the respectively desired optical effect. The typical conventional sequence for inner surface processing provides, after blocking of the spectacle lens blank by its outer surface on a block, a milling and/or turning process for producing the optically effective shape, usually followed by a fine-grinding or polishing process for achieving the requisite surface quality. 
     Use is also made in the prior art for the above-mentioned turning process of so-called fast-tool lathes in which a lathe tool can be subject to highly dynamic movement either with linear reciprocation (see, for example, U.S. Pat. No. 7,036,408 B2) or rotationally (cf., for example, document U.S. Pat. No. 6,237,452 B1), so that lens surfaces which are not rotationally symmetrical can be produced in a turning process. In order to also make this technology accessible to smaller RX workshops with comparatively small capital costs compact spectacle lens lathes having only a relative small need for set-up area have already been proposed in the prior art (U.S. Pat. No. 7,278.192 B2, U.S. Pat. 8,683,897 B2). 
     In the case of the lathe disclosed in U.S. Pat. No. 7,278,192 B2 the machine bed and the machine upper part are formed as an integral machine stand of concrete polymer with construction of all functional surfaces and spaces. In that regard, the machine bed and the machine upper part bound a central working space. With respect to the arrangement opposite the working space a fast-tool arrangement and a workpiece spindle arrangement are attached to horizontal mounting surfaces of the machine bed, the spindle arrangement being attached by way of a cross-slide arrangement extending parallel to the mounting surfaces. This machine stand does indeed have good damping characteristics, but due to the relatively large wall thicknesses of the concrete polymer has a high intrinsic weight which in this document is estimated at, for example, 1200 kilograms. 
     By contrast, a spectacle lens lathe is proposed in U.S. Pat. No. 8,683,897 B2 with a machine bed which is to weigh between 100 kilograms and 500 kilograms. In that case, the machine bed is constructed as a downwardly open cast bed with longitudinal and transverse ribs which run, in particular, in the direction of the movement axes for tool (there oscillation axis Z) and workpiece (there movement axis X), the machine bed having bearing surfaces on its upper side for the tool and workpiece drives. However, these types of cubic machine beds can be subjected to not insubstantial structural deformations under highly dynamic loads, for example due to bending and torsion of the machine bed. These deformations can then be transmitted to the tool and workpiece drives arranged above the cubic machine bed structure, so that there is a risk there of undesired axial displacements and vibrations, which can have the consequence of chatter marks or the like and ultimately inaccuracies in the workpieces being processed. 
     What is desired is a machine, which is constructed as lightly and compactly as possible, for processing optical workpieces, particularly spectacle lenses of plastic material, where the machine has a highest possible static and dynamic stiffness and in which undesired axial displacements between the axes of movement can be reliably avoided. 
     SUMMARY OF THE INVENTION 
     A machine according to one aspect of the invention for processing optical workpieces, particularly spectacle lenses of plastics material, has a machine housing enclosing a working space. The work space lies between a workpiece spindle, which is arranged at the machine housing and by ways of which the workpiece is drivable to rotate about a workpiece axis of rotation (B axis), and a fast-tool servo, which is arranged at the machine housing, for producing an oscillatory feed movement (F axis) of a lathe tool in the direction of the workpiece. A drivable carriage is provided for the workpiece spindle or the fast-tool servo, which is guided by at least two guide surfaces of a guide arrangement and by way of which a relative advance movement (X axis) between workpiece and lathe tool can be produced. The advance movement runs transversely to the feed movement (F axis) and defines therewith a processing plane (F-X plane) in which engagement between lathe tool and workpiece arises when processing takes place, and wherein the arrangement is so mounted on the machine housing that the processing plane (F-X plane) extends between the two guide surfaces. 
     The machine according to the invention thus has symmetries equally in multiple respects: in the first instance, the machine housing, which (also) takes over the functions of a machine bed, encloses the working space and at the same time bounds or forms this, so that a part of the machine housing is present on either side of the working plane. Next, the workpiece spindle and the fast-tool servo are respectively arranged on a side of the working space at the machine housing, thus are positioned with respect thereto quasi in mirror symmetry. Finally, there is a similar symmetry with the guide surfaces of the guide arrangement for the carriage, which are arranged on the machine housing on either side of the processing plane. 
     Overall, there is a structural and thermal symmetry with respect to several planes, which results not only in a very high structural stiffness of the machine, but also in substantially equal force guidance paths and thermal paths deriving from processing engagement and heat sources, for example the drives of the B, F and X axes. Any thermally-induced deformations in the carriage and/or in the machine housing in that case do not have the consequence, particularly by virtue of the arrangement in accordance with the invention of the guide surfaces with respect to the processing plane (F-X plane), of displacement of axial alignment of the workpiece (F axis) relative to the workpiece (B axis) - see, for example, U.S. Pat. No. 7,597,033 B2 with respect to processing errors (so-called “center features” or center singularities) otherwise possible in that case - even when, in particular, the fast-tool servo and the workpiece spindle heat up to different extent. The same applies to dynamic machine deformations during processing, for example as a consequence of excitation of vibration of the machine housing by the lathe tool, which oscillates at comparatively high frequencies (for example 500 Hz), at the fast-tool servo. 
     A once-set calibration of the cutter of the lathe tool, which can be mounted at the fast-tool servo with, for example, a mount as described in U.S. Pat. No. 8,166,622 B2, with respect to the workpiece axis of rotation (B axis) of the workpiece spindle is thus maintained even in the event of machine heating. This advantageously also makes possible the use of tool holders in the machine in which the position of the tool cutter has been preset outside the machine, presupposing a sufficiently precise interface between tool holder and fast-tool servo. 
     Further advantages of the machine design according to the invention are that—by comparison with the prior art outlined in the introduction—as a consequence of the high structural stiffness it is also possible to reduce the wall thicknesses of the machine housing in the sense of a lightweight construction and/or to make use of other, lighter materials for the machine housing, so that the machine is lighter overall. Thus, use can also be made—apart from, obviously, an economic grey-iron casting—of a light metal alloy, particularly an aluminum alloy, for the machine housing, which by virtue of its good thermal conductivity ensures rapid transfer of heat, whereby a stable machine operating temperature can rapidly be established. Due to the machine design in accordance with the invention the otherwise disadvantageous, comparatively high coefficient of thermal expansion of such an alloy does not have a negative influence on machine calibration. 
     The carriage is preferably substantially O-shaped as seen in cross-section and has a central receiving space for the workpiece spindle. Such a carriage is not only of very compact construction, but also has, in the case of a closed flow of force, a very high stiffness as well as, again, symmetrical thermal expansion behavior. 
     It is additionally preferable if a linear motor, which has a primary part with coils and a secondary part with magnet plates, is provided for drive of the carriage. The primary part is attached to the machine housing in long-stator mode of construction, whereas the secondary part is mounted on the carriage. In the first instance, such a linear motor is available on the market at a favorable price and without problems. Moreover, the preferred arrangement of primary part and secondary part has advantages in the sense that the heat generated by the primary part can be dissipated via the machine housing, so that cooling of the linear motor may be redundant, and that the power supply lines for the linear motor do not have be dragged by the carriage, which by comparison with a converse arrangement - equally possible in principle - not only reduces mechanical effort, but also ensures a smaller mass of the moved components and thus better acceleration behavior. 
     Various designs are conceivable for the guide arrangement for the carriage as long as it has at least two active guide surfaces, which as indicated above can be positioned with respect to the processing plane (F-X plane). Thus, the guide arrangement can be, for example, a rod guide with two cylindrical guide rods extending through the carriage, in which case each guide rod forms by its outer circumferential surface a guide surface co-operating with associated spherical bushes in the carriage. Equally possible would be, for example, a guide arrangement with only one comparatively wide guide rail having guide grooves which are arranged on opposite longitudinal sides and which each form at least one of the required guide surfaces, these co-operating with associated bearing elements. The guide rail, provided with an opening for passage of the workpiece spindle, could also be mounted at the carriage so that the guide surfaces are at the carriage, while the associated bearing elements are mounted at the machine housing. However, current preference is for a guide arrangement with two guide rails, which are mounted on the machine housing and which each form at least one of the guide surfaces. At least two, preferably four, guide shoes are fastened to the carriage and individually or in pairs are associated with a guide rail. These types of linear guides offer, with little need for constructional space, high levels of load-bearing capability, are simple to mount and are commercially available without problems, for example as type SGL-HYF from the company NB Nippon Bearing, Japan. Linear guides of the type M/V from the company Schneeberger, Switzerland, are a further alternative. 
     It is additionally preferred if one of these guide rails is arranged axially at the height of the linear motor as seen in the direction of a center axis of the machine housing, so that in advantageous manner it is capable of accepting the magnetic forces thereof without torsional moments of greater magnitude acting on the guide arrangement, and/or if the other guide rail is arranged on the side of the linear motor remote from the working space, which is conducive to a small cross-section of the machine housing perpendicularly to the center axis thereof. 
     In furtherance of the concept of the invention the fast-tool servo can be thermally conductively connected with the machine housing on either side of the processing plane (F-X plane) by way of fasteners and statically clamped in place. In this manner, the static fastening forces and dynamic forces during workpiece processing as well as heat are introduced, dissipated and otherwise act uniformly on both sides of the processing plane (F-X plane) so that mutual compensation of the effects thereof with respect to the processing plane is provided. 
     In principle, different cross-sectional shapes for the machine housing are possible without departing from the concept of the invention, for example, square, rectangular, oval, hexagonal or polygonal cross-sections. However, it is preferred, particularly with respect to good discharge of machining chips and ease of cleaning, if the working space bounded by the machine housing has a substantially circular cross-section (cylindrical boundary surface, overall barrel-shaped form) as seen in a section perpendicular to the center axis of the machine housing. 
     Moreover, the machine housing can include a housing section at the workpiece side and a housing section at the tool side, which housing sections are constructed integrally or as separate parts connected together directly or indirectly. Although fittings, seals, etc., which in the case of multi-part housing construction usually have to be provided at the connecting locations of the housing parts, are avoided by an integral housing construction, machining of an integral housing is relatively difficult in the internal region. To that extent, current preference is for a two-part housing construction in which two housing parts are directly connected together, which ensures simple capability of machining even in the internal region. However, a multi-part housing construction with more than two parts is also possible, for example a three-part housing construction with the housing section at the workpiece side as a first part, the housing section at the tool side as a second part and a section, which is, for example, tubular and radially outwardly bounds the working space, as a third part, into which the first and second parts are directly plugged on opposite sides in order to indirectly connect the latter. 
     With respect to a very high level of stiffness, a low weight and compact dimensions it is additionally preferred if the housing section at the workpiece side has similarly to a spoked wheel a tubular, substantially hollow-cylindrical inner section (hub) for receiving the fast-tool servo and a tubular, substantially hollow-cylindrical outer section (rim) surrounding the inner section, the sections being connected together by way of webs extending in spoke-like manner (spokes). 
     With regard to the housing section at the workpiece side, this preferably can have a tubular, substantially hollow-cylindrical outer section surrounding two substantially block-shaped wall sections, which are arranged substantially parallel to one another and to the center axis of the machine housing and extend up to an inner circumferential surface of the outer section and which bound therebetween a receiving space for the carriage and the drive thereof. This design again favors symmetrical transmission or dissipation of force and heat and moreover is of very compact construction. 
     In one advantageous embodiment, the substantially block-shaped wall sections respectively have an inner surface of which, for example, one is usable as support surface for the primary part of the linear motor and an outer surface, which surfaces extend substantially parallel to the center axis of the machine housing. A wall disc bounds the working space, runs substantially perpendicularly to the center axis of the machine housing, and extends peripherally up to the inner circumferential surface of the outer section to connect the inner and outer surfaces. This development is also conducive to symmetrical dissipation and transfer of force and heat. 
     With respect to a very stiff connection of the guide arrangement with the machine housing it is in that regard preferred if the substantially block-shaped wall sections respectively form, by the end faces thereof remote from the working space, on either side of the processing plane (F-X plane) a bearing surface for the guide arrangements so that the guide arrangement is based on large cross-sections with high moments of resistance, particularly with respect to bending. 
     For preference, the machine housing is provided near the fast-tool servo with a cut-out for receiving a milling spindle. Preliminary edge formation (so-called ‘cribbing’ in spectacle lenses), in a given case even finished edge formation of spectacle lenses to frame shape, can thus also be carried out by a milling tool, which is mounted at the milling spindle and protrudes into the working space, in one and the same machine. The milling spindle can optionally also be arranged to be longitudinally displaceable in its mount in the machine housing, as a result of which, for example, chamfers can be formed at the workpiece. 
     Moreover, it is also possible for the design to be such that the workpiece spindle is longitudinally displaceable (Y axis) with respect to the carriage in the direction of the workpiece axis of rotation (B axis). Consequently, further processing and/or calibration possibilities of the machine advantageously arise. On the one hand in the case of suitable angle setting of the mentioned milling spindle with respect to the processing plane (F-X plane) processing, by milling, of the end surface of the workpiece mounted on the workpiece spindle can also be carried out as described in U.S. Pat. No. 5,938,381 A, which is hereby incorporated by reference. With regard to the expanded calibration possibilities, ultimately in the case of suitable angle setting of the workpiece axis of rotation (B axis) with respect to the processing plane (F-X plane) as described in U.S. Pat. No. 7,597,033 B2 which is hereby incorporated by reference (there angle α of incidence) a highly accurate automatic alignment of the working point of the cutting edge of the lathe tool to the workpiece axis of rotation (B axis) of the workpiece spindle can take place, as also explained in detail in document U.S. Pat. No. 7,440,814 B2; which is hereby incorporated by reference with respect to this calibration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail in the following by way of preferred embodiments with reference to the accompanying, partly simplified or schematic, drawings, in which: 
         FIG. 1  shows a broken-away and partly broken open perspective view of a machine for processing optical workpieces, specifically plastics material spectacle lenses, according to a first embodiment of the invention obliquely from above and front right, with opened pivot door for access to the working space; 
         FIG. 2  shows a perspective view, which is enlarged in scale by comparison with  FIG. 1 , of the machine according to  FIG. 1  obliquely from above and back right, with closed pivot door, wherein by comparison with  FIG. 1  in addition a machine frame and casing parts were omitted so as to allow a view into the interior of the machine; 
         FIG. 3  shows a broken-away side view of the machine according to  FIG. 1  from the right in  FIG. 1 , without casing parts, but with machine frame as well as closed pivot door; 
         FIG. 4  shows a broken-away front view of the machine according to  FIG. 1 , with the simplifications of  FIG. 3 , but by comparison therewith opened pivot door; 
         FIG. 5  shows a broken-away side view of the machine according to  FIG. 1  in correspondence with the section line V-V in  FIG. 3 ; 
         FIG. 6  shows a sectional view of the machine according to  FIG. 1  in correspondence with a section line VI-VI in  FIG. 3 ; 
         FIG. 7  shows an enlarged illustration of the detail VII, which relates to the pivot door, in  FIG. 6 ; 
         FIG. 8  shows a broken-away side view of the machine according to  FIG. 1  in correspondence with the section line VIII-VIII in  FIG. 4 , but with closed pivot door; 
         FIG. 9  shows a perspective view of a machine housing of the machine according to  FIG. 1  obliquely from above and back right (tool side); 
         FIG. 10  shows a perspective view of the machine housing, which is already shown in  FIG. 9 , of the machine according to  FIG. 1  obliquely from above and front left (workpiece side); and 
         FIG. 11  shows a broken-away longitudinal sectional view of a machine for processing optical workpieces, specifically plastics material spectacle lenses, according to a second embodiment of the invention. 
     
    
    
     In the drawings, for simplification of the illustration apart from parts of the casing particularly also the control unit and control, panes, deposits for workpieces and tools, the supply devices (including lines, hoses and pipes) for current, compressed air and coolant, the coolant return as well as measuring, maintenance and safety devices have been largely omitted, since they are not necessary for an understanding of the invention. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     A CNC-controlled machine, particularly for end-face surface-processing of spectacle lenses L of plastics material, is denoted by  10  in  FIGS. 1 to 8 . The machine  10  comprises a machine frame  12 , which is illustrated only schematically and in broken-away form in  FIGS. 1, 3 to 6 and 8  and which can be constructed as a welded construction of metal sheets, with a horizontally extending upper side  14  and a vertically extending rear wall  16 , which downwardly and rearwardly bound a receiving space, which is substantially L-shaped as seen in cross-section, for a machine housing  18  described in more detail in the following. To the front, top and sides the receiving space for the machine housing  18  is bounded by a partly transparent casing  20  which is removable from the machine frame  12  and which is similarly illustrated only schematically and in broken-away form in  FIG. 1 . A machine control, a control unit, supply devices for current, compressed air and coolant as well as a device for coolant return, which are not shown in the figures, in particular, are arranged in or at the machine frame  12 . As can already be seen from  FIG. 1  and as described in more detail in the following the substantially barrel-shaped machine housing  18  is resiliently mounted on the machine frame  12  by way of a plurality of vibration-absorbing elements, here rubber-metal buffer elements  22 . 
     The machine housing  18 , which encloses or surrounds a working space  24 , in general receives the following components and subassemblies, as can be seen in, in particular,  FIGS. 1, 2, 5 and 6 : on a first side of the working space  24 , (i) a workpiece spindle  26 , by which the spectacle lens L is drivable to rotate about a workpiece axis B of rotation, and on a second side, which is opposite the first side, of the working space  24  (ii) a fast-tool servo  28  for producing an oscillatory feed movement of a rotary or lathe tool  30  or an engraving tool  30 ′ (see  FIG. 6 ) along a here linearly extending F axis in the direction of the spectacle lens L. In addition, in the illustrated embodiment the workpiece spindle  26  is mounted in (iii) a drivable carriage  32 , by which an advance movement along a linearly extending X axis can be produced between the spectacle lens L and the lathe tool  30 , the advance movement running transversely to the feed movement (F axis). For that purpose the carriage  32  is guided by at least two mounted on the machine housing  18 , which are only schematically indicated in  FIGS. 2 and 4 to 6 , because there is a difference from guide type to guide type (cf. the examples with respect thereto mentioned in the introduction) guide surfaces  34 ,  36  of a guide arrangement  38 . In addition, in the case of the illustrated embodiment there is arranged on the second side of the working space  24 , apart from the fast-tool servo  28 , additionally (iv) a milling spindle  40  which, protruding into the working space  24 , carries and drives a milling tool  42  to rotate about a tool axis C of rotation, while the spectacle lens L is suitably rotated or moved in the B and X axes, particularly for preliminary edging of the edge of the spectacle lens L in a manner known per se (so-called “cribbing”). 
     To that extent the feed movement (F axis) at the fast-tool servo  28  and the advance movement (X axis), which is produced by way of the carriage  32  at the workpiece spindle  26 , define a processing plane F-X, which is indicated in  FIGS. 4, 5 and 8  by dot-dashed lines. In the case of front-surface machining of the spectacle lens L, a substantially punctiform, machining engagement between the lathe tool  30  and the spectacle lens L takes place. At the same time the workpiece spindle  26  rotates the spectacle lens L about the workpiece axis B of rotation with generation of a cutting force, so that the desired surface shape is created at the spectacle lens L. As will be described in more detail in the following it is important that the guide arrangement  38  is mounted on the machine housing  18  in such a manner that this processing plane F-X runs between the mentioned guide surfaces  34 ,  36  so that at least one load-bearing guide surface  34  is disposed on one side, for example above the processing plane F-X, (while at least one further load-bearing guide surface  36  is disposed on another side, for example below the processing plane F-X. 
     Before the above-mentioned components and sub-assemblies, which determine the kinematics and processing possibilities of the machine  10 , as well as the arrangement thereof and fastening in the machine housing  18  are explained in more detail the last-mentioned shall be described in more detail particularly with reference to  FIGS. 9 and 10 . 
     The machine housing  18 , which in the illustrated embodiment is made of a light-metal alloy, preferably an aluminum alloy, and which is substantially rotationally symmetrical, has two parts, namely a housing section  44  at the workpiece side and a housing section  46  at the tool side, which sections are directly connected together. For that purpose, the housing section  46  at the tool side has, according to  FIGS. 5 and 6 , on its side facing the working space  24  and at the outer circumference an encircling flange surface  48 , onto which the housing section  44  at the workpiece side is pushed, with mechanically positive centering, by an encircling connecting surface  50  provided at the inner circumference. The axial relative position of the housing sections  44 ,  46  is in that case determined by an annular abutment surface  52  at the housing section  46  at the tool side, against which the housing section  44  at the workpiece side bears by an annular end face  54 . In this connecting region the housing sections  44 ,  46  are screw-connected together, which for reasons of drawing simplification is not shown. 
     The housing section  44 , which is at the workpiece side, of the machine housing  18  has a tubular, substantially hollow-cylindrical outer section  56 , at which the connecting surface  50  is formed. The outer section  56  surrounds two substantially block-shaped wall sections  58 ,  60  which are arranged parallel to one another and to the center axis M of the machine housing  18 . According to  FIG. 10  the wall sections extend up to an inner circumferential surface  62  of the outer section  56  and bound therebetween a receiving space  64  for the carriage  32 . Each block-shaped wall section  58 ,  60  is supported, on a side remote from the receiving space  64 , relative to the outer section  56  with the help of two ribs  66 . In that case the ribs  66  extend substantially over the entire width of the block-shaped wall sections  58 ,  60  as well as from this up to the inner circumferential surface  62  of the outer section  56  and in that case run substantially in radial direction as referred to the center axis M of the machine housing  18 . 
     As can be seen particularly in  FIGS. 5 and 10 , the block-shaped wall sections  58 ,  60  each have an inner surface  68 ,  70  and an outer surface  72 ,  74 , which run substantially parallel to the center axis M of the machine housing  18  and in the direction of the working space  24  are connected with a wall disc  76  bounding the working space  24 . The wall disc  76  runs substantially perpendicularly to the center axis M of the machine housing  18  and extends peripherally up to the inner circumferential surface  62  of the outer section  56 . Between the block-shaped wall sections  58 ,  60  the wall disc  76  according to  FIG. 5  has a thicker wall thickness and is there provided with an elongate cut-out  78 , which is substantially rectangular as seen in plan view, for passage of the workpiece spindle  26 . 
     As  FIGS. 5 and 10  best show, as seen going from the working space  24  in the direction of the center axis M of the machine housing  18  the upper block-shaped wall section  58  is axially recessed somewhat relative to an end face  80  at the outer section  56  of the housing section  44  at the workpiece side, whereas the lower block-shaped wall section  60  axially protrudes somewhat relative to the end face  80 . At its end faces remote from the working space  24  the block-shaped wall sections  58 ,  60  each form on either side of the processing plane F-X a respective bearing surface  82  or  84  for the guide arrangement  38 . As a consequence of the above discussed different lengths of the block-shaped wall sections  58 ,  60  in the direction of the center axis M of the machine housing  18 , the bearing surface  82  at the upper block-shaped wall section  58  is disposed axially above the inner surface  70  of the lower block-shaped wall section  60 . 
     According to, in particular,  FIG. 8  the working space  24  bounded by the machine housing  18 , more precisely the inner circumferential surface  62  of the outer section  56  of the housing section  44  at the workpiece side, has a substantially circular cross-section as seen in a section perpendicular to the center axis M of the machine housing  18 . The outer section  56  of the machine housing  18  is provided in a base region of the working space  24  with a substantially oval (see also  FIG. 6 ) drain opening  86  for coolant and waste material removal, through which waste material and coolant can run off into a coolant container (not shown) arranged below the machine housing  18  in the machine frame  12 . 
     In forward direction, i.e. towards an operator position, the working space  24  is provided over about a quarter of the cylindrical circumference of the outer section  56  with an access opening  88 , which is rectangular as seen in a development and which can be selectably covered by a manually actuable pivot door  90 . The preferably at least partly transparent pivot door  90 , which is provided with a handle  92 , is in that case curved just like the machine housing  18  and is guided in guide tracks  94 , which are formed at the outer circumference of the outer section  56  on both sides of the access opening  88  and which are closed by strip-shaped sheet-metal covers  95  screw-connected with the machine housing  18 . 
     Further details of the housing section  46 , which is at the tool side, of the machine housing  18  are shown clearly in  FIGS. 1, 3 to 6 and 9 . Accordingly, the housing section  46  at the tool side has a tubular, substantially hollow-cylindrical inner section  96  for reception of the fast-tool servo  28  and a tubular, substantially hollow-cylindrical outer section  98  surrounding the inner section  96 , the sections being connected together by way of webs  100  extending in spoke-like manner. As can be seen in  FIG. 3 , the inner section  96  in that case is arranged to be somewhat eccentrically offset with respect to the outer section  98  and thus to the center axis M of the machine housing  18 . The webs  100  in the illustrated embodiment eight in number extend with respect to a web number of nine in distribution with substantially uniform angular spacing over the circumference approximately radially to the direction of movement of the lathe tool  30 , i.e. with respect to the F axis of the fast-tool servo  28 . Towards a side at the right in  FIGS. 3 and 9  the inner section  96  is provided with a cut-out  102  in order to create a space for receiving the milling spindle  40  near the fast-tool servo  28 . In this space the “ninth” web as considered in the circumferential distribution of the webs  100  is absent. 
     As seen going out from the working space  24  along the center axis M of the machine housing  18  the inner section  96  is formed to be longer than the outer section  98 . The webs  100  are in that case so shaped and chamfered that they extend substantially over the entire length not only of the inner section  96 , but also of the outer section  98 . As seen towards the working space  24  along the center axis M of the machine housing  18  the webs  100  end at a multiply stepped terminating wall region  104  of the housing section  46  at the tool side. The terminating wall region  104  is, according to  FIG. 9 , provided with a passage opening  106  for the tools mounted on the fast-tool servo  28  and adjacent thereto with a further passage opening  108  for the milling spindle  40 , but otherwise the structure formed from the inner section  96 , outer section  98  and webs  100  is closed towards the working space  24 . 
     The components and subassemblies, in particular those already mentioned in the introduction, are now mounted as follows at or in the machine housing  18  so far described The milling spindle  40  is received in the cut-out  102  of the machine housing  18  and flange-mounted in a manner, which is not shown in more detail, on the terminating wall region  104  of the housing section  46  at the tool side. It passes with suitable sealing through the passage opening  108  in the terminating wall region  104  (see  FIG. 9 ) so that it projects into the working space  24 , as can be seen particularly in  FIG. 6 . The milling tool  42  is drivably mounted on the milling spindle  40  and regulated in rotational speed, to rotate about the tool axis C of rotation, which in the illustrated embodiment lies in a plane together with the F axis of the fast-tool servo  28  and the X axis of the workpiece spindle  26 . 
     The fast-tool servo  28  received in the inner section  96  of the housing section  46  at the tool side is thermally conductively connected with the machine housing  18  on both sides of the processing plane F-X by way of fasteners and statically fixed. More precisely, the fast-tool servo  28  according to  FIG. 3  is mounted at the bottom on a metallic base plate  110 , which in turn is secured to the inner section  96  of the machine housing  18 . Two metallic cylinder-segment blocks  112  are arranged on the fast-tool servo  28 , which is substantially square as seen in cross-section, which blocks can be urged apart to both sides by an interposed straining screw  114  and thus pressed against an inner circumferential surface  116  of the inner section  96 . It is apparent that the cylinder-segment blocks  112  in that case at the same time press the fast-tool servo  28  downwardly against the base plate  110 . As a result, the fast-tool servo  28  is not only clamped very rigidly in the machine housing  18 , but also fastened in such a manner that the heat generated in/by the fast-tool servo  28  is readily dissipated by way of the base plate  110  and the cylinder-segment blocks  112  to both sides of the processing plane F-X in the machine housing  18 . In an alternative (not shown), the fast-tool servo can also have a substantially cylindrical housing, which, optionally with lubrication by a thermally conductive grease, is mechanically positively fitted in the inner section of the machine housing and suitably fixed there. 
     As seen in axial direction, the fast-tool servo  28  bears against the terminating wall region  104  of the machine housing  18 , wherein at least the tool or tools mounted at the fast-tool servo  28  passes or pass with suitable sealing through the passage opening  106  provided in the terminating wall region  104  (cf.  FIG. 9 ) and protrude into the working space  24 , as can be seen in, for example,  FIG. 6 . In that case, the tools  30 ,  30 ′ are mounted on the fast-tool servo  28  by way of, for example, a mount  118 , as is known from U.S. Pat. No. 8,166,622 B2 which is hereby incorporated by reference, for the avoidance of repetition construction and functioning of the mount. This mount  118  can advantageously also be pre-adjusted outside the machine  10 . 
     The internal construction and the functioning of the fast-tool servo  28  shown here are otherwise described in detail in U.S. Pat. No. 8,056,453 B2 which is hereby incorporated by reference for the avoidance of express repetition. The tools  30 ,  30 ′ are positionally controlled, in particular can be movable under oscillation along the F axis, by the fast-tool servo  28 . 
     The carriage  32  according to  FIG. 2  has a substantially O-shaped cross-section, with a central receiving space  120  for the workpiece spindle  26 . The workpiece spindle  26  extends through the receiving space  120  and is fastened in this in suitable manner (not shown) or alternatively directly integrated together with the carriage as spindle housing (similarly not illustrated). At the end remote from the working space  24  the workpiece spindle  26  in the illustrated embodiment carries a pneumatic relief cylinder  122  for a spring-biased collet chuck  124 , which is known per se and which serves the purpose of clamping the spectacle lens L, which is blocked on a block member, in the working space  24  to the workpiece spindle  26  for rotational entrainment. The workpiece spindle  26  extends by its collet chuck end into the working space  24 , in which case it passes through the cut-out  78  in the wall disc  76  of the machine housing  18  (see  FIG. 10 ). The open cross-section between workpiece spindle  26  and cut-out  78  is in that case variably bridged over with the assistance of a stainless-steel slat cover  126  with a rear-side bellows and sealed towards the working space  24 . By way of the workpiece spindle  26 , the spectacle lens L mounted thereon is drivable, with control in angular position, to rotate about the workpiece axis B of rotation. The rotational measuring system required for that purpose is not shown in more detail. 
     The carriage  32 , which in the direction of the X axis carries a rubber-elastic abutment buffer  128  on both sides, is drivable by a linear motor  130 . The linear motor  130  has a primary part  132  with coils and a secondary part  134  with magnet plates. Whereas the primary part  132  is fastened in long-stator mode of construction to the machine housing  18 , more precisely on the inner surface  70  of the block-shaped wall section  60  of the machine housing  18 , in which case the primary part  132  extends in the direction of the X axis approximately over the entire width of the inner surface  70  acting also a cooling surface, the secondary part  134  in the figures is mounted from below on the carriage  32  above the primary part  132 . 
     The guide arrangement  38  for the carriage  32  can be best seen in  FIGS. 2, 5 and 6 . In the illustrated embodiment (guide from the company NB, as mentioned in the introduction) it comprises two guide rails  136 ,  138  and in total four guide shoes  140 ,  142 , which are associated in pairs with the guide rails  136 ,  138 . The guide rails  136 ,  138  are fastened to the machine housing  18  in parallel arrangement and, in particular, on the bearing surfaces  82 ,  84  of the block-shaped wall sections  58 ,  60 , wherein the guide rails  136 ,  138  extend in the direction of the X axis approximately over the entire width of the bearing surfaces  82 ,  84 . Thereagainst, the guide shoes  140 ,  142 , which are in engagement with the guide rails  136 ,  138 , are in the figures mounted at the bottom and top in pairs adjacent to one another on the carriage  32 . It is thus ensured that the carriage  32  is guided on both sides, i.e. here both above and below the processing plane F-X, on the guide surfaces  34 ,  36 . 
     According to, in particular,  FIG. 5  the upper guide rail  136  with the guide surfaces  34  is arranged above, i.e. axially at the height of, the linear motor  130  as seen in the direction of the center axis M of the machine housing  18 , so that with respect to the linear motor  130  there is no lever arm by way of which the linear motor  130  could exert, by its magnetic forces, rotational or torsional moments on this guide rail  136 . Moreover, according to  FIG. 5  the lower guide rail  138  with the guide surfaces  36  is arranged in space-saving manner on the side of the linear motor  130  remote from the working space  24 . This is all made possible by the afore-described design of the comparatively thick, block-shaped wall sections  58 ,  60  of the machine housing  18 , which moreover have almost the same clear spacing from the center axis M of the machine housing  18 . 
     It remains to be noted to the carriage  32 , the guidance and drive thereof, that the workpiece spindle  26  is movable with positional control along the X axis by these subassemblies. The linear travel measuring system required for this purpose is denoted in  FIGS. 2, 4 and 5  by  144 . 
     As, finally, can be inferred from  FIGS. 3 to 6 , the rubber-metal buffer elements  22  are so arranged that the rearward two rubber-metal buffer elements  22 , which are mounted on the rear wall  16  of the machine frame  12 , lie in the processing plane F-X, whereas the lower two rubber-metal buffer elements  22  mounted on the upper side  14  of the machine frame  12  are disposed, as seen in the direction of the X axis, at the axial height of the fast-tool servo  28 . As seen in the direction of the F axis the rubber-metal buffer elements  22  are axially mounted at the height of the fast-tool servo  28  or of the linear motor  130 . Overall, the afore-described machine  10  has, with respect to constructional space requirement, weight, thermosymmetry, force/heat flow, dynamic stiffness, vibration damping, thermal stability (operation without a cooling unit is optionally possible) and working space encapsulation, a substantially improved construction relative to previously known concepts for smaller machines in the spectacle lens industry. 
     The edge processing, by milling, of the spectacle lens L mounted on the workpiece spindle  26  by the milling tool  42  with the assistance of the positionally controlled B axis (in angle), and the positionally controlled X axis and the C axis of the machine  10 , which is regulated in rotational speed does not require any further explanation at this point, since it is familiar to the person ordinarily skilled in the art. The same applies to the lathe processing of the optically active surface of the spectacle lens L by the lathe tool  30 , which takes place with the assistance of the positionally controlled B (in angle), F and X axes of the machine  10 . 
     Finally, the second embodiment shall be described, with reference to  FIG. 11 , only to the extent that it significantly differs from the first embodiment explained in detail above with reference to  FIGS. 1 to 10 , wherein the same or corresponding components or subassemblies are provided with the same reference numerals. 
     As already mentioned in the introduction, the second embodiment is constructed to be expanded relative to the first embodiment with respect to further processing and calibration possibilities, namely in particular in the respect that the workpiece spindle  26  is longitudinally displaceable relative to the carriage  32  in the direction of the workpiece axis B of rotation (additional Y axis). 
     For that purpose the workpiece spindle  26  is initially mounted by a bearing bush  146 , which can be, for example, an aerostatic bearing, a spherical bush or a slide bearing, in the receiving space  120  of the carriage  32  to be longitudinally displaceable. In addition, fastened at or in the carriage  32  is a rotary drive  148 , for example a hollow-shaft servomotor, which is operatively connected by way of a threaded drive  150  (threaded spindle, threaded drive nut) with a holder  152 , which in turn is mounted on the workpiece spindle  26 . Through rotation of the threaded spindle by way of the rotary drive  148  it is thus possible to displace the workpiece spindle  26  relative to the carriage  32  in order to move it further into or out of the working space  24 , for example in order to carry out milling processing also at the end face of the spectacle lens L (for which purpose obviously also the milling tool would have to be suitably adjusted). As an alternative, use could also be made here of a linear motor (not shown) for producing this linear movement. This movement also takes place with CNC positional control along the Y axis. The linear travel measuring system required for that purpose is not, however, shown in  FIG. 11 . 
     Moreover, in the case of the second embodiment the base plate  110  is of wedge-shaped construction as seen from the side or in section, so that the F axis in correspondence with the wedge angle is positioned obliquely at a work angle α with respect to the workpiece axis B of rotation, whereby a corresponding angular position between the processing plane F-X and a movement plane, which is defined by the axes X and Y, of the workpiece spindle  26  results. The sense and purpose of this inclined setting namely calibration of the cutting height of the lathe tool  30  with respect to the workpiece axis B of rotation under suitable drive of the F and Y axes are described in detail in to U.S. Pat. No. 7,597,033 B2 which is hereby incorporated by reference for avoidance of express repetition. 
     A machine for processing of, in particular, spectacle lenses of plastics material has a machine housing enclosing a working space, which lies between a workpiece spindle for rotational driving of the spectacle lens about a workpiece axis of rotation (B axis) and a fast-tool servo for generating an oscillatory feed movement (F axis) of a lathe tool in the direction of the spectacle lens. Provided for the workpiece spindle is a drivable carriage, which is guided at at least two guide surfaces of a guide arrangement, for producing a relative advance movement (X axis) between spectacle lens and lathe tool, which advance movement extends transversely to the feed movement and defines therewith a processing plane (F-X plane), in which engagement between lathe tool and spectacle lens takes place for the processing. In order to achieve a very compact and stiff design of the machine the guide arrangement is so mounted on the machine housing that the processing plane extends between the two guide surfaces. 
     Variations and modifications are possible without departing from the scope and spirit of the present invention as defined by the appended claims.