Patent Publication Number: US-6902467-B2

Title: Apparatus for processing a lens and process for processing a lens

Description:
This application claims priority from Japanese Patent Application No. 2002-157047, filed May 30, 2002, the entire disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to an apparatus for processing a lens, which is used for processing the peripheral portion of a lens such as a spectacle lens to provide a prescribed shape so that the lens can be fitted into a the lens portion of a spectacle frame. 
     BACKGROUND OF THE INVENTION 
     Heretofore, when a lens such as a spectacle lens is processed so that the lens is fitted into the lens portion of a spectacle frame, the peripheral face of an uncut lens is ground by a grinder or cut by a cutter, and the uncut lens is formed into a prescribed shape of the peripheral portion in accordance with data of the shape of the lens portion of the spectacle frame. 
     Examples of a known processing apparatus for this purpose include, as disclosed in Japanese Patent Application Laid-Open No. 2002-18686, apparatuses in which a rotating tool (a grinder), which can be freely rotated and grinds the peripheral face of the lens, is disposed around a first shaft on a base. The position of grinding or cutting is set by driving a second shaft supporting the lens, which can be freely swung relative to the first shaft of the rotating tool, towards the first shaft of the rotating tool by an arm, and rotating the lens around the axis of the second shaft. 
     These apparatuses are equipped with a control portion in which selections are made among the types of processing such as the flat processing and the beveled processing and selection among the modes of processing are made such as the crude processing, finishing, mirror finishing, grooving and chamfering. The pressure of chucks and the tools used for the processing are set in accordance with the material of the lens (glasses, plastics, polycarbonates and acrylic resins). The peripheral portion of the lens is processed based on shape data of the lens frame. 
     In recent years, various types of resins are used for the lens so that the refractive index is increased and the impact resistance is improved. Processability is different depending on the material. 
     In the conventional apparatuses described above, processing is conducted by setting the processing condition such as the direction of rotation of the lens axis (the up cut and the down cut) and the presence or the absence of water supply in accordance with the material of the lens. When a lens made of a new material is processed, occasionally, the conditions which can be set are insufficient, and processing cannot be conducted smoothly. 
     For example, as disclosed in Japanese Patent Application Laid-Open Nos. 2000-511231 and 2002-504935 (PCT National Phase Applications), the processing of a lens exhibiting excellent impact resistance such a lens made of a polyurethane-based resin, which is formed with a polyurethane material prepared from an aliphatic diisocyanate compound, an intermediate compound having hydroxyl group selected from polyester glycols, polyether glycols and mixtures of these glycols and a curing agent of an aromatic primary diamine, has certain problems. For example, melted dust and debris of grinding having the shape of ribbons and strings is occasionally attached at the peripheral portion of the processed lens in both of wet processing using cooling water and dry processing without using cooling water, and the dust and debris at the peripheral portion of the lens must be manually removed after the processing has been conducted. This procedure increases the time and the labor required for the processing of the lens. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome the above problem and it is another object to achieve sure based on shape data of lens portion of a spectacle frame independently of the material of the lens. 
     In accordance with the above objects, there is provided an apparatus for processing a lens displaces a lens supported by a holding shaft relatively to a main shaft equipped with a rotating tool and processes a peripheral portion of a spectacle lens in accordance with shape data of a lens frame. The apparatus comprises: a means for adjusting a load that changes a load of pressing the lens to the rotating tool; a means for driving a lens shaft that changes a rotational speed and a direction of rotation of the holding shaft; a means for cooling that injects a cooling liquid to the lens; a means for setting processing conditions that sets controlling conditions of the means for adjusting a load, the means for driving a lens shaft and the means for cooling, in every step of processing the lens; and a means for control that controls the means for adjusting a load, the means for driving a lens shaft and the means for cooling based on the controlling conditions set by the means for setting processing conditions. The processing can be conducted under the load, the relative directions of rotation of the lens and the rotating tool (the up cut or the down cut) and the condition of injection of cooling water in accordance with the material of the lens, which may be different in each case. 
     Also in accordance with the above objects, there is provided a process for processing a lens, comprising: displacing a lens for spectacles made of a resin and supported by a holding shaft relatively to a main shaft having a rotating tool and processing a peripheral portion of the lens in accordance with shape data of a lens frame. The lens made of a resin is formed with a polyurethane material which is prepared from an aliphatic diisocyanate compound, an intermediate compound having hydroxyl group which is selected from polyester glycols, polyether glycols and mixtures of the glycols and a curing agent of an aromatic primary diamine. In the processing, the lens is pressed to the rotating tool under a load set at a value of 2 kgf or greater and smaller than 3 kgf, the injection of the cooling liquid is stopped, and rotation of the holding shaft and rotation of the main shaft are set to be in the same direction. 
     In accordance with the present invention, since the load can be set as desired, not only conventional materials such as glasses, CR-39 and polycarbonates but also new materials can be processed. Since the direction of the processing (the up cut or the down cut) and the condition of water supply can be changed in every step of the processing such as the rough grinding and the finishing, materials requiring different conditions in every step can be surely processed. 
     In one embodiment, the material of the lens is a polyurethane material which is prepared from an aliphatic diisocyanate compound, an intermediate compound having hydroxyl group which is selected from polyester glycols, polyether glycols and mixtures of the glycols and a curing agent of an aromatic primary diamine. In this embodiment, melting (attachment) of dust and debris of grinding is prevented and the processing can be conducted smoothly by pressing the lens to the rotating tool under a load of 2 kgf or greater and smaller than 3 kgf and processing in the up cut condition in which the rotation of the holding shaft and the rotation of the main shaft are set in the same direction. 
     In accordance with a further embodiment there is provided an apparatus for processing a lens. The apparatus comprises a lens holding unit displaceable in a vertical direction and having a lens shaft arranged to hold a lens to be processed. Also provided is a main shaft unit equipped with a rotating tool and disposed to processes a peripheral portion of a spectacle lens held in the lens holding unit in accordance with shape data of a lens portion of a spectacle frame, when the lens holding unit is displaced to contact a lens held in the lens holding unit with the rotating tool. A load adjusting device is provided equipped to adjust a load pressing the lens to the rotating tool. A lens shaft drive is connected to drive the lens shaft with a changeable rotational speed and direction of rotation. A cooling device is arranged to inject a cooling liquid toward a lens held in the lens shaft. A means is provided for setting processing conditions for the load adjusting device, the drive and the cooling device, having an output. A control means is provided for controlling the load adjusting device, the drive and the cooling device based on output from the means for setting processing conditions. 
     In accordance with yet another embodiment, the means for setting processing conditions sets in advance controlling conditions in a plurality of processing steps for a plurality of lens materials. 
     In accordance with a still further embodiment, the means for control comprises a means for switching a cooling condition which switches between running and stopping of injection of the cooling liquid by the cooling device during the processing and the means for setting processing conditions sets running or stopping of injection in a plurality of processing steps. 
     In accordance with yet another embodiment, the apparatus further comprises a main shaft drive connected to drive the main shaft unit with a changeable rotational speed; and the means for setting processing conditions sets a rotation speed of the main shaft in a plurality of processing steps and the means for control controls the main shaft drive based on the output of the means for setting processing conditions. 
     In accordance with a still further embodiment of the invention, there is provided a process for processing a lens, comprising the steps of: (a) supporting a lens on a shaft of a lens support unit; (b) displacing the lens relatively to a main shaft having a rotating tool and processing a peripheral portion of the lens in accordance with shape data a lens portion of a spectacle frame; wherein the processing further comprises the steps of: (c) rough grinding by pressing the lens to the rotating tool under a load set in advance and grinding the lens roughly; and (d) finishing by pressing the lens to the rotating tool under a load set in advance, wherein the finishing is started without injection of a cooling liquid, and completed with injection of the cooling liquid. 
     In another embodiment, the process further comprises changing the load accordance with a material of the lens. 
     In yet another embodiment, the lens is formed with a polyurethane-based resin, the loads are set at a value of 2 kgf or greater and smaller than 3 kgf, and rotation of the holding shaft and rotation of the main shaft are set in same direction. 
     In a still further embodiment, there is provided a process for processing a lens comprising the steps of: supporting a resin lens with the lens holding shaft of a lens holding unit; displacing the lens relatively to a main shaft having a rotating tool and processing a peripheral portion of the lens in accordance with shape data of lens portion of a spectacle frame; wherein the processing further comprises the steps of pressing the lens to the rotating tool under a load set in advance, stopping injection of a cooling liquid and setting rotation of the lens holding shaft and rotation of the main shaft in the same direction; and wherein the lens comprises a polyurethane material prepared from an aliphatic diisocyanate compound, an intermediate compound having hydroxyl group which is selected from polyester glycols, polyether glycols and mixtures of the glycols and a curing agent of an aromatic primary diamine. 
     In yet another embodiment, the load is set at a value of 2 kgf or greater and smaller than 3 kgf. 
     Further objects, features and advantages of the present invention will become apparent from the Detailed Description of Illustrative Embodiments, which follows, when considered together with the attached figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An illustrative embodiment of the present invention will be described as follows with reference to Figures. 
         FIG. 1  shows a perspective view of the appearance of the apparatus for processing a lens according to one embodiment of the present invention. 
         FIG. 2  shows a perspective view exhibiting the main portions of the inner construction of the apparatus according to an embodiment of the present invention. 
         FIG. 3  shows a perspective view exhibiting the inner construction of the apparatus of an embodiment of present invention with the measuring unit and the finishing unit removed. 
         FIG. 4  shows a right side view exhibiting the inner construction of an embodiment of present invention. 
         FIG. 5  shows a sectional view of the elevating and lowering unit and the lens unit in the vertical direction when the processing is started. 
         FIG. 6  shows a sectional view of the elevating and lowering unit and the lens unit in the vertical direction when the processing is completed. 
         FIG. 7  shows a sectional view of the elevating and lowering unit and the lens unit in the horizontal direction when the lens is held by the lens-holding shafts. 
         FIG. 8  shows a perspective view exhibiting the relation between the unit for controlling the load and the lens unit. 
         FIG. 9  shows a table describing the relationship between the amount of unwinding the wire and the position of the lens unit using the load as a parameter. 
         FIG. 10  shows a schematic front view of the cooling unit of an embodiment of present invention. 
         FIG. 11  shows a schematic diagram exhibiting the control portion of an embodiment of present invention. 
         FIG. 12  shows a block diagram exhibiting the operation portion and the control portion. 
         FIG. 13  shows an expanded view of the lens and the main rotating tool during the processing. 
         FIG. 14  shows a diagram exhibiting the steps of processing the lens. 
         FIG. 15  shows an example of the table of the conditions of the processing in accordance with the material of the lens, wherein (A) shows the table for the rough grinding and (B) shows the table for the finishing. 
         FIG. 16  shows a diagram exhibiting the difference in the conditions of the processing in accordance with the material of the lens using the relations between the rotation speed of the main shaft or the condition of water supply and the time, wherein (A) shows the diagram for the rough grinding and (B) shows the diagram for finishing. 
     
    
    
     DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
     The invention will now be described in terms of certain illustrative embodiments and with reference to the figures in which like reference numerals are given like meanings. 
     In  FIG. 1 , at the right side of the front of the apparatus for processing a lens  10  contained in a case having the shape of a rectangular parallelpiped  11 , an operation portion  13  for selecting or inputting the conditions for processing the lens and a display portion  12  for displaying information on the processing such as the data of the shape of the lens frame and the data for the processing are disposed. The operation portion  13  comprises touch panels, touch switches, keys or the like. The display portion  12  comprises an LCD, CRT, or the like. 
     At the front center of the apparatus for processing a lens  10 , a door  14  is disposed that can be opened or closed as desired and used for inserting or taking out a lens. 
     After the entire apparatus is described, the constituent portions will be described in detail. 
     Outline of the Apparatus 
     In  FIG. 2 , a base unit  2  that can be displaced in a direction parallel to a main shaft  51  having a main rotating tool  50  (a main means for processing) (the direction of the X-axis in the Figure) is disposed inside of the case  11 . The base unit  2  supports a lens unit (a lens-holding unit)  4  that can be displaced in the vertical direction (in the direction of the Z-axis in the Figures). 
     In  FIG. 2 , the transverse direction of the apparatus for processing a lens  10  is assigned to the X-axis, the vertical direction (the direction of the height of the apparatus) is assigned to the Z-axis, and the direction from the left to the right in  FIG. 4  (the direction towards the inside of the apparatus) is assigned to the Y-axis. It is assumed that these axes orthogonally intersect each other. 
     In the lens unit  4 , a lens-holding shaft  41 , that is divided into two portions and selectively holds the center of the lens  1  between the two portions, is disposed in a manner such that the lens-holding shaft can be freely rotated. The lens-holding shaft  41  is placed on the vertical line of the main rotating tool (a grinder or a cutter)  50  that is supported by a shaft on a base plate  15 . The lens-holding shaft  41  and the main shaft  51  of the main rotating tool  50  are arranged parallel to each other along the X-axis. The lens  1  is held by the lens-holding shaft  41  so that the face of the lens  1  is placed along a plane perpendicular to the axial line of the lens holding shaft. 
     A measuring unit  6  comprising styluses  60  and  61  for measuring positions on the concave face and the convex face, respectively, of the lens  1  is fixed on the vertical line of the lens-holding shaft  41 . 
     The styluses  60  and  61  are displaceable in a direction parallel to the lens-holding shaft  41 . For the measurement of the position of the lens  1  after being completely processed and the thickness of the peripheral edge, the styluses  60  and  61  are brought into contact with both faces of the lens  1  when the lens unit  4  is elevated. The lens unit  4  is elevated or lowered in accordance with the data of the shape of the lens frame while the lens-holding shaft is rotated and the displacements of the styluses  60  and  61  in the axial direction are detected by linear scales or the like that are not shown in the Figure. 
     For processing the lens  1 , starting from the condition shown in  FIG. 2 , the lens unit  4  is lowered after the main rotating tool  50  is rotated and the peripheral portion (the outer peripheral portion) of the lens  1  is ground into the prescribed shape by elevating or lowering the lens unit  4  in accordance with the shape data of the lens frame while the lens-holding shaft  41  is rotated. 
     By elevating or lowering the lens unit  4 , based on the shape data of the lens frame corresponding to the rotation angle of the lens-holding shaft  41 , continuous grinding is conducted to a processing depth in accordance with the rotation angle of the lens  1 . During processing, the force of pressing the lens  1  to the main rotating tool  50  (the processing pressure) is provided by the weight of the lens unit  4  itself. The adjustment of the load in accordance with the material of the lens is conducted by supporting a portion of the weight of the lens unit  4  by a unit for controlling the load  8  disposed at a position above the lens unit  4 . 
     The position of contact between the lens  1  and the main rotating tool  50  is changed by displacing the base unit  2  in the direction of the X-axis in FIG.  1  and selection between the flat grinding and the beveled grinding can be made. Switching between the rough grinding and the finishing grinding can also be made similarly. 
     A finishing unit  7  (a means for finishing) which comprises a rotating tool for chamfering  70  and a rotating tool for grooving  71  and can be displaced in the direction of the Y-axis (in the inner direction of the apparatus) is disposed at a position above the lens unit  4 . When the finishing unit  7  is at the advanced position, the rotating tool for chamfering  70  and the rotating tool for grooving  71  are placed at a position directly above the lens-holding shaft  71 . The selection between the rotating tools  70  and  71  is made and the position of the processing is set by elevating the lens unit  4  and driving the base unit  2  in the direction of the X-axis. Finishing is conducted in this condition. 
     The portions of the apparatus according to the illustrative embodiment will be described in more detail as follows. 
     Main Shaft Unit 
     In  FIGS. 2 and 3 , the main shaft  51  on which the rotating tool (a grinder or a cutter having diamonds or the like)  50  is disposed and a motor  55  for driving the main shaft  51  are fixed to the base plate  15  inside of the case  11 . The main shaft unit comprises these members as main components. 
     The main shaft  51  is, as shown in  FIG. 2 , supported by a shaft on the base plate  15  along the X-axis in a manner such that the main shaft  51  can be rotated freely and is disposed parallel to the lens-holding shaft  41 . 
     At an end portion of main shaft  51 , a main rotating tool  50  for mechanically processing, the lens  1  is attached. The main rotating tool  50  is placed at the central portion in the direction of the X-axis in FIG.  2  and at the front side of the apparatus (at the lower left side in FIG.  2 ). The base end portion of the main shaft (at the right side in  FIG. 2 ) is driven by a motor  55  via a belt  57  and pulleys. 
     In the main rotating tool  50  that mechanically processes the lens  1 , as shown in  FIG. 2 , a rough grinder  50   a , a finishing grinder for flat grinding  50   b , a finishing grinder for beveled grinding  50   c  and a grinder for mirror finishing  50   d  are disposed successively from the side of the tip of the main shaft  51  (the left side in the Figure). Depending on the material of the lens  1 , an electrodeposited diamond wheel or a sintered diamond wheel, for example, is used as the rough grinder  50   a , a sintered diamond wheel, for example, is used for the finishing grinder for flat grinding  50   b  and the finishing grinder for beveled grinding  50   c , and a sintered diamond wheel, for example, is used for the grinder for mirror finishing  50   d . The types and the positions of these grinders can be suitably exchanged with each other by detachment and attachment. 
     Base Unit 
     A base unit  2  for driving the lens unit  4  in the direction of the X-axis is disposed at a position inside the main shaft  51  in  FIG. 2  (in the direction of the Y-axis, at the right side in FIG.  2 ). 
     As shown in  FIG. 3 , the base unit  2  comprises a base  20  that can be displaced in the direction of the X-axis, and a servomotor  25  (hereinafter, referred to as an X-axis motor) that controls positioning by driving the base  20  in the direction of the X-axis. 
     The base  20  is disposed on guide members  21  and  22 , which are fixed on the base plate  15  in the direction of the X-axis so that the base  20  can be freely displaced. Therefore, the base  20  can be freely displaced in the direction of the X-axis. 
     In  FIG. 3 , an inner screw  23  is disposed at a position below the base  20  between the guide members  21  and  22  so that the inner screw  23  can be rotated freely. An outer screw  24  fixed at the lower face of the base  20  is engaged with the inner screw  23  and the base  20  is driven in the direction of the X-axis by rotation of the screw  23 . 
     One end of the inner screw  23  and the X-axis motor  25  are connected to each other via a gear and a cogged belt  26  and the base  20  is positioned in the direction of the X-axis in accordance with the rotation angle of the X-axis motor  25 . 
     Elevating and Lowering Unit 
     As shown in  FIGS. 3 and 5 , for example, two poles  401  and  402  stand on the base  20 , penetrate a frame  40  of the lens unit  4  and guide the lens unit  4  in the vertical direction (the direction of the Z-axis) so that the lens unit  4  can be displaced freely. 
     As shown in  FIGS. 3 and 5 , the lens unit  4  is driven in the vertical direction and positioned in the vertical direction by the elevating and lowering unit  3 , which is displaced in the direction of the Z-axis. The lens unit  4  is positioned in the direction of the X-axis by the base unit  2 . The lens unit  4  supporting the lens  1  is driven in the directions of the X-axis and the Z-axis relative to the main shaft  51 . 
     The elevating and lowering unit  3  comprises, as shown, for example, in  FIGS. 3 ,  4  and  5 , a screw  31  that is supported by a shaft on the base  20  between the poles  401  and  402  and that penetrates the frame  40  of the lens unit  4  in the vertical direction, a positioning member  34  that is engaged with the screw  31  at an inner peripheral portion and can support the lens unit  4  by contacting the frame  40  of the lens unit  4  at the upper end, and a servomotor  33  (hereinafter, referred to as a Z-axis motor) that is connected to the lower end of the screw  31  via a cogged belt  32  and a gear. The elevating and lowering unit  3  is disposed on the base  20 . 
     In the elevating and lowering unit  3 , the screw  31  is rotated by driving the Z-axis motor  33 . The positioning member  34  having an outer screw  35  engaged with the screw  31  is thus driven in the direction of the Z-axis. The outer screw  35  is displaced in the direction of the Z-axis since the rotating movement in the circumferential direction is restricted by a mechanism on the lens unit  4 , as shown later. 
     As shown in  FIG. 5 , the positioning member  34  contacts the inner periphery of a hole portion  40 A formed in the frame  40  of the lens unit  4  in the vertical direction in a manner such that the positioning member  34  can slide and make a relative displacement in the vertical direction. 
     At the upper end of the hole portion  40 A, a ceiling portion  400  connected to the frame  40  is disposed. As shown in  FIGS. 3 and 6 , at the side of the outer screw  35  of the positioning member  34 , a stopper  36  standing in the direction of the Z-axis is disposed so that the stopper  36  can contact the lower face of the ceiling portion  400 . 
     In  FIG. 3 , the stopper  36  protruding from the upper portion of the positioning member  34  contacts the lower face of the ceiling portion  400  and the load of the lens unit  4  applied by the ceiling portion  400  is supported by the positioning member  34  comprising the stopper  36  and the outer screw  35 . The outer screw  35  and the stopper  36  are connected to each other at each base portion through a base  340 . 
     As shown in  FIGS. 5 and 6 , the hole portion  40 A of the frame  40  has a sectional shape such that the positioning member  34  and the stopper  36  are stopped by each other around the Z-axis (in the direction perpendicular to the plane of  FIG. 6 ) and the idle rotation of the outer screw  35  by the rotation of the screw  31  is prevented. In other words, the stopper  36  fixed at the side of the outer screw  35  is arrested by the hole portion  40 A and the rotation of the positioning member  34  is prevented. Thus, the outer screw  35  is elevated or lowered by the rotation of the screw  31  and the positioning member  34  is displaced in the direction of the Z-axis due to this movement. 
     When the stopper  36  does not contact the ceiling portion  400 , as shown in  FIG. 5 , the lens  1  supported by the lens unit  4  is brought into contact with the main rotating tool  50  and the weight of the lens unit  4  itself is applied as the load. The upper end face  34 A of the positioning member  34  and the lower face of the ceiling portion  400  do not contact each other and a prescribed gap is formed. 
     At a position below the ceiling portion  400  facing the gap, a hole portion  421 , where one end of a sensor arm  300  (a means for amplifying a relative displacement) for detecting completion of the processing of the lens unit (in the vertical direction) is inserted, is disposed along the Y-axis in the Figure in a manner such that the hole portion  421  penetrates the frame  40  across the hole portion  40 A. 
     The sensor arm is, as shown in  FIGS. 5 and 6 , an integrally formed arm having the shape of an inverse L which is composed of an arm  301  extending to the left side in the Figures (in the direction of the Y-axis) and inserted into the hole portion  421  and an arm  302  extending in the lower direction in the Figure (in the direction of the Z-axis, to the side of the base  20 ). The arm  301  and the arm  302  are disposed approximately perpendicularly to each other. The length of the arm  302  in the vertical direction is set longer than that of the arm  301  in the horizontal direction. 
     A bending portion  303  at the middle of the sensor arm  300  having the shape of an inverse L is supported by a shaft  420  disposed at the ceiling portion  400  of the lens unit  4  in a manner such that the bending portion  303  can freely swing around the shaft  420  and, therefore, the sensor arm can swing around the X-axis. 
     Between the arm  302  extending in the direction of the Z-axis and the ceiling portion  400 , a spring  310  is disposed that pushes the arm  301  extending in the direction of the Y-axis in the lower direction in  FIGS. 5 and 6  (in the counter-clockwise direction in the Figures). 
     Since the arm  301  inserted into the hole portion  421  crosses the hole portion  40 A in the direction of the Y-axis, a penetrating portion through which the screw  31  is inserted is formed and the lower face of the arm  301  facing the inner periphery of the hole portion  40 A can be brought into contact with or separated from the upper end face  34 A of the positioning member  34 . 
     Since the sensor arm  300  is pushed in the counter-clockwise direction in the Figures by the spring  310 , as shown in  FIG. 5 , the tip  301 A of the arm  301  is brought into contact with the lower side of the hole portion  421  and stopped there in the condition that the upper end face  34 A of the positioning member  34  and the arm  301  are separated from each other (in the condition that the stopper  36  is separated from the ceiling  400 ). 
     On the other hand, as shown in  FIG. 6 , when the stopper  36  of the positioning member  34  contacts the ceiling portion  400  of the lens unit  4  (in the condition that the stopper  36  contacts the ceiling portion  400  as shown in FIG.  3 ), in other words, when the positioning member  34  supports the lens unit  4 , the upper end face  34 A of the positioning member  34  pushes the arm  301  in the upper direction. In this condition, the sensor arm  300  rotates and the arm  302  extending in the direction of the Z-axis is placed at the prescribed position (for example, a position in the vertical direction as shown in FIG.  6 ). 
     A bracket  422  protruding along the lower portion of the sensor arm  300  (the arm  302 ) is disposed at the frame  40 . At a prescribed position of the bracket  422  that faces the lower end of the arm  302  swinging around the X-axis, a sensor is disposed for detecting completion of the processing (a means for detection)  320 . The sensor detects the free end portion of the arm  302  swinging around the X-axis. The free end portion means the end portion of the sensor arm  300  that is detected by the sensor for detecting completion of the processing  320  and, in the present embodiment, is the end portion of the arm  302 . 
     The sensor for detecting completion of the processing  320  comprises, for example, a photosensor such as a photointerruptor. As shown in  FIG. 6 , when the swinging arm  302  comes to the prescribed position (the position in the vertical direction where the lens unit  4  and the positioning member  34  are brought into contact with each other) and the light of the photointerruptor of the sensor for detecting completion of the processing is interrupted, the sensor is switched at ON and it is detected that the processing has been completed. 
     The elevating and lowering unit  3  supports the lens unit  4  in the elevating direction. After the lens unit  4  starts the processing of the lens  1 , the processing depth (the processing amount) is decided in accordance with the position of the elevating and lowering unit  3  in the direction of the Z-axis. When the prescribed processing depth is achieved, the sensor for detecting completion of the processing  320  is switched at ON. The proceeding of the processing can be detected at every rotation angle of the lens  1  in this manner and, when the output of the sensor for detecting completion of the processing at the entire peripheral portion of the lens  1  shows ON, it is decided that the processing has been completed on the entire peripheral portion of the lens  1 . 
     Since the relative distance between the position of the lens unit  4  in the vertical direction and the position of the positioning member  34  in the vertical direction (the processing depth) is amplified by the lever ratio described above in the swing of the arm  302 , the sensor for detecting completion of the processing  320  detects, with great accuracy, that the prescribed processing depth has been reached. As described above, the elevating and lowering unit  3  supports the lens unit  4  in the direction of elevation and, after the processing of the lens  1  has been started by the lens unit  4 , the processing depth (the processing amount) is decided in accordance with the position of the elevating and lowering unit  3  in the direction of the Z-axis. 
     Lens Unit 
     The lens unit  4  is displaced by the elevating and lowering unit  3  in the direction of the Z-axis is, as shown in  FIGS. 2 and 7 , and guided by the two poles  401  and  402  standing on the base  20  in the vertical direction (in the direction of the Z-axis). In this manner, the lens unit can be freely displaced. The lens unit comprises the lens-holding shaft  41  that is divided into two portions, a motor for driving the lens  45  that rotates the lens-holding shaft  41 , and a motor for the lens chuck  46  that changes the pressure of the lens-holding shaft  41  to hold the lens  1 . 
     As shown in  FIG. 4 , the lens-holding shaft  41  that holds and rotates the lens  1  is placed at a position directly above the main rotating tool  50 . The direction connecting the axial line of the lens-holding shaft  41  and the axial line of the main shaft  51  is in the vertical direction. 
     As shown in  FIGS. 2 and 7 , arms  410  and  411  protruding from the frame  40  of the lens unit  4  in the direction of the front of the apparatus (to the lower left side of FIG.  2 ). Frame  40  and the arms  410  and  411  form a rectangle having three sides and open on one side. The arms  410  and  411  support the lens-holding shaft  41 . 
     In  FIGS. 3 and 8 , the lens-holding shaft  41  is divided into two portions at the center, i.e., a shaft  41 R supported by the arm  410  and a shaft  41 L supported by the arm  411 . The arm  41 L is supported by the arm  411  at the left side in  FIG. 8  so that the arm  41 L is freely rotateable. The arm  41 R is supported by the arm  410  at the right side in  FIG. 8  so that the arm  41 L is freely rotateable and can be displaced in the axial direction (in the direction of the X-axis). 
     The shafts  41 L and  41 R are rotated by the motor  45  for driving the lens via cogged belts  47 ,  48  and  49 . The cogged belts  47  and  48  are connected to each other through a shaft  430  and the rotation angles of the shafts  41 L and  41 R are synchronized. 
     For this purpose, a gear  432  engaged with the cogged belt  47  is fixed to the shaft  41 L and a gear  431  engaged with the cogged belt  48  is fixed to the shaft  41 R. So that the shaft  41 R can be displaced relative to the arm  410  in the direction of the X-axis, the shaft  41 R is arrested in the direction of rotation by the key  433  disposed between the shaft  41 R and the inner periphery of the gear  431  and, on the other hand, can be relatively displaced in the direction of the X-axis. 
     In  FIG. 7 , a chuck mechanism driven by a motor for the lens chuck  46  is disposed at the end portion (at the right side in  FIG. 7 ) of the shaft  41 R. 
     Then, to decide the processing depth in accordance with the rotation angle of the lens  1 , the shaft  41 L penetrates the arm  411  and a slit plate  143  is fixed at the end portion protruding from the arm  411 . By detecting the position of rotation of the slit plate  143  by a photosensor  145  (a lens position sensor, or a means for detecting the angle) fixed to the arm  411 , the position (the rotation angle) of the lens  1  held by the lens-holding shaft  41 L is detected. 
     In the lens unit  4  having the construction described above, when the lens  1  is fixed at the receiver of the lens holder  141 , the motor for the lens chuck  46  is driven and the lens-holding shaft  41 R is moved to the left side of FIG.  9 . The lens  1  is fixed by pressing the lens  1  by the lens presser  142  under pressure. 
     When the lens  1  is processed or when the finished position of the peripheral portion of the lens  1  is measured, the lens-holding shaft  41 L and  41 R are rotated by driving the motor for driving the lens  45  and the lens  1  is rotated. 
     As shown in  FIG. 2 , the main rotating tool  50  is fixed to the base plate  15  and is not displaced. The lens  1  supported by the lens unit  4  is displaced in the vertical direction relative to the main rotating tool  50  by the displacement of the elevating and lowering unit  3  in the direction of the Z-axis and the processing can be conducted to the desired depth. 
     The position of the lens  1  for the processing can be changed by changing the rotation angle of the motor for driving the lens  46  and the peripheral portion of the lens  1  can be processed to the desired processing depth. 
     The tool used for the processing can be changed by changing the position of contact between the lens  1  and the main rotating tool  50  by the displacement of the base  20  in the direction of the X-axis. 
     Unit for Controlling the Load 
     The unit for controlling the load (for adjusting the load)  8  for controlling the pressure of pressing the lens  1  supported by the lens unit  4  to the main rotating tool  50  will be described. 
     The unit for controlling the processing pressure  8  is, as shown in  FIGS. 4 and 8 , fixed on an upper base  200  which is disposed at upper ends of poles  401  to  404  standing on the base plate  2  and is displaced in the direction of the X-axis in combination with the lens unit  4 . 
     In  FIGS. 4 and 8 , the unit for controlling the load  8  comprises pulleys  82  and  82  driven by a motor for controlling the load  81  (an actuator), wires  83  wound around the pulleys  82 , and springs (an elastic member)  84  connecting the wires  83  to the frame  40  of the lens unit  4 . The motor for controlling the load  81  and the pulleys  82  and  82  are connected to each other via a worm gear  87 . 
     In  FIG. 8 , the lens unit  4  is suspended with pairs of pulleys  82  (winding members), the wires  83  (suspending members) and the springs  84 . The numbers of the wire  83  and the spring  84  can be selected as desired. 
     The force of pressing the lens  1  to the main rotating tool (the load, the pressure of grinding) is the weight of the lens unit  4  itself. However, since it is necessary that the load (the surface pressure) be changed in accordance with the material of the lens for processing (e.g., either a glass or a resin) and the thickness of the peripheral portion, a portion of the weight of the lens unit  4  is supported by the tension of the springs  84  and the load of the lens unit  4  applied to the lens  1  is thus adjusted. 
     Since the lens is processed while the lens unit  4  is displaced vertically, it is necessary that an approximately constant load be applied independently of the position of the lens unit  4 . 
     Therefore, the amount of unwinding the wires  83  is adjusted by the motor for controlling the load  81  in accordance with the displacement of the lens unit in the direction of the Z-axis so that the tension of the springs  84  is held approximately constant. 
     In  FIG. 8 , the amount of unwinding the wires  83  is controlled in accordance with the rotation angle and the number of rotation of the pulleys  82  which are detected by the slit plate  85  disposed coaxially with the pulleys  82  and a photosensor  86  detecting the passage of the slit. 
     As the position of the lens unit  4  in the direction of the Z-axis, the amount of driving the Z-axis motor  42  (for example, the output of the encoder in the case of a servomotor and the number of steps in the case of a step motor) or a value obtained by directly measuring the position of the lens unit  4  or the lens-holding shaft  41  along the Z-axis can be used. 
     As for the relation between the amount of unwinding the wires  83  (or the amount of driving the motor for controlling the load  81 ) and the load applied to the lens  1 , the tension of the springs  84  decrease and the load increases as the amount of unwinding the wires  83  increases, and the tension of the springs  84  increases and the load decreases as the amount of unwinding the wires  83  decreases. 
     As for the relation between the position of the lens unit  4  in the direction of the Z-axis and the amount of unwinding the wires  83 , the amount of unwinding can be decreased as the lens unit is elevated at a higher position and the amount of unwinding the wires  83  can be increased as the processing by the lens unit  4  proceeds using a linear table or the map shown in FIG.  9 . 
     Since the required load varies depending on the material and the thickness of the peripheral portion of the lens  1  as described above, as will be described later, the load can be selected based on a plurality of properties shown in FIG.  9 . These properties include material input data and the thickness of the peripheral portion of the lens or the relationship between the amount of unwinding and the position of the lens unit  4  (a proportional relationship obtained by calculation). 
     Since the thickness of the peripheral portion varies depending on the position of processing, different properties may be selected in accordance with the rotation angle of the lens-holding shaft  41  (the position of processing the lens). 
     The position of the lens unit in the direction of the Z-axis is decided by the elevating and lowering unit  3  described above. As shown in  FIG. 13 , since the processing is conducted while the lens  1  supported by the lens-holding shaft  41  is rotated, the position in the direction of the Z-axis always changes. As shown in  FIGS. 5 and 6 , the position of the lens unit  4  at the start of the processing is different from that at the end by the processing depth. 
     When the amount of unwinding the wires  83  is controlled in accordance with the change in the rotation angle of the lens  1  or the processing depth, the control and the mechanism become complicated due to the detection of the actual position of processing. 
     By disposing springs  84  between the wires  83  and the frame  40  of the lens unit  4 , the load close to the set value can be maintained by the change in the length of the springs  84  even when the amount of unwinding the wires  83  cannot follow the change in the position of the lens unit  4 . Therefore, the load of calculation required for the control can be decreased remarkably. 
     G. Cooling Unit 
     The cooling unit for supplying a cooling liquid during the processing of the lens will be described as follows. The cooling unit is used for cooling the uncut lens  1  and the tools and removes dust and debris of grinding. In the present embodiment, a cooling liquid comprising water as a main component is used. 
     The cooling unit comprises, as shown in  FIGS. 10 and 2 , a waterproof case  101  that has the shape of a box and surrounds the main rotating tool  50 , the lens  1  supported by the lens-holding shaft  41 , the styluses  60  and  61  and the rotating tools  70  and  71  of the finishing unit  7 , a nozzle  102  injecting the cooling liquid to the vicinity of the lens  1  held by the lens-holding shaft  41 , a tank  103  disposed at a position below the waterproof case  101 , and a pump  104  sending the cooling liquid in the tank  103  to the nozzle  102  under a pressure. 
     On the waterproof case  101 , a door  14  which can be opened and closed is disposed (refer to FIG.  1 ). When the door  14  is opened, the lens is attached or detached. When the door is closed, the inside of the waterproof case  101  is tightly closed and wetting of the bearing of the main shaft  51 , the motors, the power source and the electric circuits with the scattered cooling liquid injected in the waterproof case  101  is prevented. 
     The cooling liquid used for cooling the lens  1  and the rotating tools during the processing returns to the tank  103 , is sucked into the pump  104  and circulated. Since the cooling liquid used for cooling the lens  1  contains dust and debris formed by processing the lens  1 , a drain which can be opened and closed is attached to the tank  103 , so that the dust and debris formed by cutting can be removed and the cooling liquid can be exchanged with the fresh cooling liquid. 
     H. Control Unit 
     The apparatus for processing a lens  10  comprises the various mechanisms (units) described above and further has a control portion  9  for controlling the mechanisms as shown in FIG.  11 . 
     In  FIG. 11 , the control portion  9  comprises a microprocessor (CPU)  90 , a means for memory (a memory, a hard disk and the like)  91 , and an I/O control portion (an interface)  92  connected to the motors and the sensors. The control portion  9  reads the shape data of the lens frame sent from the apparatus for measuring the shape of the frame  900  placed at the outside. The control portion  9  also reads, the data from various sensors and drives the various motors so that the prescribed processing is conducted based on the properties (the material, the hardness and the like) of the lens  1  set by the operation portion  13 . As the apparatus for measuring the shape of the frame, an apparatus such as the apparatus disclosed in Japanese Patent Application Laid-Open No. Heisei 6(1994)-47656 can be used. 
     The control portion  9  comprises a servomotor control portion  93  that positions the lens unit  4  in the directions of the X-axis and the Z-axis by driving the X-axis motor  25  of the base unit  2  and the Z-axis motor  42  of the elevating and lowering unit  3 . 
     The motor  55  for driving the main rotating unit  50 , the motor for finishing  72  which drives the rotating tools  70  and  71  and the pump  104  of the cooling unit are each connected to the I/O control portion  92  via driving portions  901 ,  902  and  903 , respectively, and the condition of rotation or the speed of rotation is controlled in accordance with the direction from the microprocessor  90 . The driving portion  901  of the motor  55  of the main shaft is constituted, for example, with an inverter and the main rotating tool  50  is driven at the desired speed of rotation. 
     The motor for the lens chuck  46  that controls the holding pressure applied to the lens  1  by changing the length of the shaft  41 R of the lens-holding shaft  41  is connected to the I/O control portion  92  via a driving portion  911  which controls the holding pressure in accordance with the electric current of driving. 
     The motor  45  for driving the lens is connected to the I/O control portion  92  via a driving portion  912  which controls the rotation angle of the lens-holding shaft  41  (the lens  1 ). The microprocessor  90  directs the position of processing the lens  1  based on the data of the shape of the lens frame obtained from the apparatus for measuring the shape of the frame  900 , detects the rotation angle of the lens  1  by the sensor for detecting the position of the lens  145  and drives the Z-axis motor  42 , so that the processing depth in accordance with the rotation angle based on the shape data of the lens frame is achieved. 
     When the prescribed processing depth is achieved, a sensor for detecting completion of processing  320 , which will be described later, is switch at ON and the actual position of processing is fed back to the microprocessor  90 . 
     The motor for driving the finishing unit  73  that drives the finishing unit  7  in the direction of the Y-axis, the motor for driving styluses  62  that drives the styluses  60  and  61  of the measuring unit  6 , and the motor for controlling the processing pressure  81  of the unit for controlling the load  9  are each connected to the I/O control portion  92  via driving portions  913 ,  914  and  915 , respectively, which control the positioning. 
     The outputs of linear scales  600  and  601  connected to the styluses  60  and  61 , respectively, of the measuring unit  6  are input into a counter  920 . The microprocessor  90  reads the values in the counter  920  and measures the position of the peripheral portion (the position of the finished portion) of the lens  1 . 
     A photosensor  86  (a sensor for the position of the wire) of the unit for controlling the load  8  detects the rotation angle of the pulley  82 . The microprocessor  90  drives the motor for controlling the load  81  in a manner such that the load set in accordance with the position of the lens unit  4  in the direction of the Z-axis is maintained. 
     The operation portion  13  disposed at the front of the cover of the apparatus for processing a lens  10  is connected to the I/O control portion  92  and transfers the directions from the operator (the material of the lens  1  and the processing with or without the beveled processing or the grooving) to the microprocessor  90 . The microprocessor  90  outputs the response to the directions and the information of the content of the processing to the display portion  12  via the driving portion  921 . 
     An embodiment of the operation portion  13  and the content of the processing will be described as follows. 
       FIG. 12  shows a block diagram exhibiting the function of the operation portion  13  and the control portion  9 . The operation portion  13  comprises a means for manual setting  13 A for manually setting the conditions of the processing and a means for presetting  13 B in which the conditions of the processing set in advance are classified with respect to the material. 
     The means for manual setting  13 A comprises a portion for setting the processing mode  130  that selects the step of the processing from steps such as rough processing, finishing (the flat finishing or the, beveled finishing) and mirror finishing (the flat mirror finishing or the beveled mirror finishing), a portion for setting the rotation speed of the main shaft  131  which sets or selects the rotation speed of the main shaft  51 , a portion for setting the rotation speed of the lens  132  which sets or selects the rotation speed of the lens-holding shaft  41 , a portion for setting a load  133  which sets or selects the load (kgf) applied to the lens  1  by the lens unit  4  and a portion for setting the condition of water supply  134  which sets or selects the condition of the use of the cooling water. 
     At the portion for setting the processing mode  130 , for example, one of rough processing, finishing (the flat finishing and the beveled finishing), mirror finishing (the flat mirror finishing and the beveled mirror finishing), chamfering and grooving is selected using ten keys or touch switches. The value set at the portion for setting the processing mode  130  is input into a portion for selecting the tool in the control portion  9  and the position of the lens unit  4  in the direction of the X-axis is set so that the lens  1  is placed at the position corresponding to the tool for the selected processing mode. 
     At the portion for setting the rotation speed of the main shaft  131 , a desired rotation speed (rpm) is input using key input, for example, ten keys, or a desired rotation speed is selected from a plurality of speeds (such as high, medium and low) set in advance using touch switches. The value set at the portion for setting the rotation speed of the main shaft  131  is input into a portion for setting the rotation speed of the mains shaft  941  of the control portion  9  and the control parameter is, set so that the motor is controlled at the set value. 
     At the portion for setting the rotation speed of the lens shaft  132 , a desired rotation speed (rpm) is input using keys or other input methods, or a desired rotation speed is selected from a plurality of speeds set in advance using touch switches. The value set at the portion for setting the rotation speed of the lens shaft  132  is input into a portion for setting the rotation speed of the lens  942  in the control portion  9  and the control parameter is set so that the motor for driving the lens  45  is controlled at the set value. 
     At the portion for setting the rotation speed of the lens shaft  132 , the direction (positive or negative) of rotation of the lens-holding shaft  41  can also be set. For example, when the direction of the rotation is positive, the lens-holding shaft  41  and the main shaft  51  are rotated in the same direction and the grinding is conducted as an up cut and, when the direction of the rotation is negative, the lens-holding shaft  41  and the main shaft  51  are rotated in different directions and the grinding is conducted as a down cut. In the up cut, for example, as shown in  FIG. 13 , the lens-holding shaft  41  and the main shaft  51  are both rotated in the clockwise direction and the lens  1  and the rotating tool  50  at the main shaft  51  are displaced in different directions at the position of the grinding. In the down cut, the movements are reversed and the lens  1  and the rotating tool  50  at the main shaft  51  are displaced in the same direction at the position of the grinding. 
     At the portion for setting a load  133 , a desired load (kgf) is input, or a desired load is selected from a plurality of loads (such as high, medium and low) set in advance using touch switches. The value set at the portion for setting a load  133  is input into a portion for deciding the properties  943  in the control portion  9  and the driving pattern of the motor for controlling the load  81  is set so that load is controlled at the set value as shown in FIG.  9 . 
     At the portion for setting the condition of water supply  134 , a pattern of water supply is selected from a plurality of patterns of water supply set in advance using touch switches. For example, a pattern of water supply is selected from no water supply at all (dry processing), continuous water supply (wet processing) and water supply started during the processing. The value set at the portion for setting the condition of water supply  134  is input into a portion for deciding the pattern  944  of the control portion  9  and the pattern of driving the pump  104  is set so that the water supply is controlled in accordance with the set pattern of water supply. 
     By the means for presetting  13 B, the pattern of the processing is set in advance in accordance with the material of the lens  1 . For example, there is provided a switch for selecting glass  135 , a switch for selecting a generally used resin such as CR-39  136  (Plastic  1  in the Figure), a switch for selecting a hard resin for lenses such as polycarbonates  137  (Plastic  2  in  FIG. 15 ) and a switch  138  for selecting a resin which produces melted dust and debris of grinding as described above (Plastic  3 , in FIG.  15 ). When one of these switches  135  to  138  is selected, the rotation speed of the main shaft, the rotation speed of the lens shaft, the load and the pattern of water supply are set into a table  945  in the control portion  9  for every processing mode. 
     Fine adjustment can be made for each processing mode by selection using the means for manual setting  13 A after one of the selection switches  135  to  138  in the means for presetting  13 B has been pushed in accordance with the material of the lens. 
     The processing decided by the means for manual setting  13 A or the means for presetting  13 B can be started by pushing a starting button not shown in the Figure. 
     Although not shown in the Figures, the operation portion  13  may further comprise a portion for setting the chuck pressure, for setting the driving power of the motor for the lens chuck  46  and a portion for controlling the chuck pressure for setting the control parameters in accordance with a set value so that the pressure of holding the lens  1  can be changed as desired. 
     I. Outline of the Processing 
     The procedures of the processing by the apparatus for processing a lens  10  using the control portion described above will be described in the following with reference to FIG.  14 . 
     In  FIG. 14 , the procedures conducted by the control portion  9  after the lens  1  is set into the lens-holding shaft  41  are shown. The data of the shape of the lens frame are read at the apparatus for measuring the shape of the frame  900  and the position for the grinding is calculated. After the conditions of the processing set at the operation portion  13  is read, in step S 1 , the shaft  41 R of the lens-holding shaft  41  is displaced to the position for holding the lens  1  by driving the motor for the lens chuck  46  and the lens  1  is held under a pressure in accordance with the material of the lens  1 . The lens unit  4  is elevated or lowered in accordance with the data of the shape of the lens frame and is positioned at the prescribed position for the measurement. 
     In step S 2 , the styluses  60  and  61  are brought into contact with the convex face  1   a  and the concave face  1   b , respectively, of the lens  1  by driving the motor  62  for driving the styluses. The lens  1  is rotated by driving the motor for driving the lens  45 . The lens unit  4  is elevated or lowered to the position in accordance with the rotation angle of the lens  1  (the position of the complete processing on the peripheral portion of the lens) based on the data of the shape of the lens frame (the data of the peripheral portion of the lens  1 ) and the position of the complete processing on the lens  1  is measured and stored into the means of memory  91 . 
     When the measurement is completed, rough grinding is conducted in step S 3 . The lens unit  1  is moved to the prescribed position relative to the main rotating tool  50  (for example, the position directly above the rough grinder  50   a  in  FIG. 2 ) by driving the base unit  2  and the elevating and lowering unit  3 . Rough grinding is conducted by driving the motor  55  at the prescribed rotation speed and the lens  1  is formed into an approximately the same shape as that of the lens frame. During the processing, the load, the rotation speed of the lens shaft and the pattern of water supply are controlled based on the set values. 
     When the rough grinding is completed, flat finishing or beveled finishing is conducted in accordance with the presence or the absence of a bevel using the main rotating tool  50  based on the set values (steps S 4  and S 8 ). 
     When finishing is completed, mirror finishing is conducted, if desired, using the main rotating tool  50  based on the set values (steps S 5  and S 9 ). 
     When the above grinding is the flat grinding, the grooving of the peripheral face of the lens is conducted using the rotating tool  71  (step S 6 ). In the final step, the chamfering of the peripheral portion of the lens is conducted using the rotating tool  70  (step S 7 ). A series of processing steps are completed as described above. 
     J. Setting of the Conditions of the Processing 
     The setting of the conditions of processing by the operation portion  13  and the control portion  9  described above will be described as follows. 
       FIG. 15  shows an example of the setting of the table  945  shown in FIG.  12 . FIG.  15 (A) shows a table for rough grinding and FIG.  15 (B) shows a table for finishing. 
     For glass, CR-39 (Plastic  1 ) and polycarbonates (Plastic  2 ) which are known materials, the conditions of the processing are set in advance, for example, as follows: the grinding speed: 1,000 m/min; the rotation speed of the lens shaft: 5 to 6 rpm; the direction of the grinding: down cut; the load: 3.5 to 4 kgf; dry processing without water supply in the rough grinding; and wet processing with continuous water supply in the finishing. (When the value is shown by a range, the central value is used for the setting.) 
     As described above, in the case of a new material for a lens such as a material for a lens made of a thermosetting resin and exhibiting a great resistance to grinding, heretofore, a satisfactory processing could not be achieved due to occasional attachment of dust and debris of grinding having the shape of ribbons and strings to the peripheral portion of the lens after the rough grinding in any of dry processing and wet processing when values for conventional materials such as the values for glass or Plastic  2  shown in Table 15(A) are used. 
     In the case of a lens exhibiting excellent impact strength which is formed with a polyurethane material prepared from an aliphatic diisocyanate compound, an intermediate having hydroxyl group selected from polyester glycols, polyether glycols and mixtures of these glycols and a primary aromatic diamine curing agent as disclosed by Japanese Patent Application (as a national phase under PCT) Laid-Open Nos. 2000-511231 and 2002-504935, as described above, the lens has the problem that melted dust and debris of grinding having the shape of ribbons and strings is occasionally attached to the peripheral portion of the processed lens when processing is conducted using a conventional apparatus. Furthermore, processing conducted after the above step such as finishing, chamfering and grooving is occasionally adversely affected. 
     The dust and debris of grinding removed from the peripheral portion of the lens is occasionally attached to and accumulated at the inner periphery of the apparatus and adversely affect the movement of the tools and the lens. 
     An example of the lens described above is formed with a polyurethane which is obtained by reacting a polyester glycol or a polyether glycol having a weight-average molecular weight of about 600 to about 1,200 with 4,4′-methylenebis(cyclohexyl isocyanate) in relative amounts by equivalent of 2.5 to 4.5 NCO per OH and preferably 3 to 3.5 NCO per OH to form a prepolymer, followed by reacting the formed prepolymer with a curing agent of an aromatic diamine in relative amounts by equivalent of 0.95 to 1.02 NH 2 /1.0 NCO and preferably 0.96 to 1.0 NH 2 /1.0 NCO. The lens made of the resin having the above composition will be referred to as the polyurethane lens having difficulty in grinding. 
     In the conventional apparatus described above, the load cannot be set as desired. Even when the load can be changed, the load can be changed in the direction of increasing the load from the ordinary value (about 3.5 to 4.0 kgf), i.e., in the direction of decreasing the time of processing, such as a load of 4.0 kgf or greater, but cannot be changed to a value smaller than the ordinary value (3.5 kgf). Therefore, conditions for preventing the formation of the dust and debris of grinding having shapes of ribbons and strings are hard to find in the processing of a difficult to-grind polyurethane lens. 
     As the result of the experiment of grinding using the apparatus for processing a lens of the present invention, it was found that, when the difficult-to-grind polyurethane lens having difficulty in grinding was processed under loads of grinding decreased from the ordinary value (about 3.5 to 4.0 kgf) as shown in the following Table, the attachment of melted dust and debris of grinding did not take place and the dust and debris became powder under loads smaller than 3 kgf. An excellent finished face could be obtained in the above conditions. The melting of the dust and debris could be prevented and the size of the dust and debris decreased when the load was further decreased. However, the time of the processing increased due to the decrease in the load. It was found by the experiment that both of the processability and the time of processing could be satisfactory when the load was 2 kgf, which is smaller than the ordinary value. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Load (kgf) 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 2 
                 2.5 
                 2.75 
                 3 
                 3.5 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Melting of dusts of 
                 none 
                 none 
                 none 
                 slight 
                 marked 
               
               
                 grinding 
               
               
                   
               
               
                 (The rough grinding, the dry processing and the up cut)  
               
            
           
         
       
     
     It was also found that up cut and dry processing were necessary as the conditions in Table 1. In either down cut or wet processing, the melting of the dust and debris of grinding took place. As the rotating tool  50  used above, an electrodeposited diamond wheel was preferable to a sintered diamond wheel due to the more excellent grinding properties. 
     Since the load of the apparatus for processing a lens can be changed as desired by the unit for adjusting the load  8  and materials in a wide range can be treated by the operation portion  13 , the polyurethane lens having difficulty in grinding can be surely processed by setting the rotation speed of the main shaft, the rotation speed of the lens shaft, the direction of grinding (the direction of rotation of the lens shaft), the load and the pattern of water supply as desired. 
     In the control table of the unit for controlling the load  8  shown in  FIG. 9 , the characteristic line L 1  corresponds to a load of 4 kgf, the characteristic line L 2  corresponds to a load of 3.5 kgf and the characteristic line L 3  corresponds to a load of 2 kgf. 
     When the values shown in FIGS.  15 (A) and  15 (B) are set as Plastic  3  in the switch  138  of the means for presetting, the difficult-to-grind lens can be processed more easily. 
     In rough grinding of the difficult-to-grind lens, melting of the dust and debris of grinding can be surely prevented when the load is set at a value smaller than 3 kgf, dry processing is conducted in the up cut condition, the speed of grinding is increased to a value greater than the ordinary value of 1,000 m/min by 10% or greater, and the rotation speed of the lens shaft is increased to a value about twice as fast as the ordinary value. The speed of grinding changes depending on the relative rotating speeds of the main shaft and the lens shaft. In the above, the rotation speed of the lens shaft is neglected since the rotation speed of the lens shaft is much smaller than the rotation speed of the main shaft. For setting an accurate speed of grinding, the rotation speed of the lens shaft and the direction of the rotation (the direction of the grinding) are taken into consideration. When the outer diameter φ of the main rotating tool is constant, the rotating speed of the main shaft may be listed in the table in place of the speed of grinding. 
     In finishing the difficult-to-grind lens, as shown by Plastic  3  in FIG.  15 (B), the speed of grinding and the rotation speed of the lens shaft are changed to ordinary values (glass˜Plastic  2 ) and the condition of water supply is changed from dry processing to wet processing started during the processing while the load and the direction of grinding are kept the same as those in the rough grinding. Excellent finishing can be achieved in a decreased time under these conditions. 
     It is preferable that the time when dry processing is changed to wet processing during processing is in the final step or in the later steps of processing. For example, dry processing can be changed to wet processing when the margin for grinding reaches 0.1 to 0.2 mm in the radial direction. For the finishing of the difficult-to-grind lens, a conventionally used sintered diamond grinder for finishing can be used as the rotating tool  50 . It is preferable that the speed of grinding and the rotation speed of the lens shaft are changed when the rotating tool  50  is changed. 
     When the above conditions of the processing are set at the selection switch  138  of the means for presetting and the rough grinding and the finishing of the lens  1  are conducted, the relations between the speed of grinding (the rotation speed of the mains shaft) or the condition of water supply and the time are as shown in FIG.  16 . 
     For rough grinding, dry processing is conducted at a great speed of grinding (for example, 1,256 m/min) as shown in FIG.  16 (A). When rough grinding is completed, as shown in FIG.  16 (B), the speed of grinding is decreased and the finishing is started in accordance with the dry processing. At the time t in the final step of finishing, the supply of water is started and the cooling liquid is injected toward the lens  1 . Thus, the processing is converted into wet processing in the later stage of finishing. 
     Since the desired load can be set by the unit for controlling the load  8 , the processing can be conducted not only for conventional materials such as glasses, CR-39 and polycarbonates but also for new materials. Since the direction of processing (up cut or down cut), the speed of grinding and the condition of water supply can be changed at every step such as the rough grinding and the finishing, the processing can be conducted surely even when the conditions of the processing are different among the steps as shown for the difficult-to-grind lens. 
     In the above embodiment, the weight of the lens unit  4  is adjusted in accordance with the tension of the spring  84  in the unit for controlling the load  8 . Alternately, an elastic material may be used as the wire  83  in place of the spring  84 . 
     In the above embodiment, the unit for controlling the processing pressure  8  has the construction such that the lens unit  4  is suspended from an upper position. Alternatively, the lens unit  4  may be pushed from a lower position to the upward direction. 
     In the above embodiment, the unit for controlling the load  8  Alternatively, the lens unit  4  may be directly suspended by the wire  83  and the load applied to the lens  1  may be adjusted in accordance with the force of driving or the amount of driving of the motor  81 . 
     In the above embodiment, the apparatus for processing a lens is the so-called apparatus of the vertical movement which conducts the processing with the displacement of the lens  1  in the vertical direction. The present invention can also be applied to an apparatus which conducts the processing by supporting the lens by an arm swinging relative to the main shaft in the conventional manner. 
     While the present invention has been described in terms of illustrative embodiments, one of ordinary skill in the art will recognize that additions, deletions, substitutions and improvements can be made while remaining within the scope and spirit of the present invention, as defined by the appended claims.