Abstract:
An eyeglass lens grinding apparatus for grinding a periphery of a lens to be processed. The apparatus includes: a lens rotation shaft which holds and rotates the lens; a lens rotating device having a lens rotating motor and a first transmission member which transmits a rotational torque of the lens rotating motor to the lens rotation shaft; an abrasive wheel rotation shaft which rotates a lens grinding abrasive wheel; and an abrasive wheel rotating device having an abrasive wheel rotating motor and a second transmission member which transmits a rotational torque of the abrasive wheel rotating motor to the abrasive wheel rotation shaft. A moving device causes a relative movement between the lens rotation shaft and the abrasive wheel rotation shaft to vary an axis-to-axis distance between an rotation axis of the lens rotation shaft and an rotation axis of the abrasive wheel rotation shaft, thereby brining the lens into pressure contact with the abrasive wheel for processing. A detector detects a state of rotation of the lens or the abrasive wheel. A controller judges whether the lens has been completely processed, based on a result of detection by the detector.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an eyeglass lens grinding apparatus for grinding the periphery of an eyeglass lens. 
     An eyeglass lens grinding apparatus is known. After a subject lens is chucked by two lens rotating shafts, the apparatus controls the axis-to-axis distance between an axis of the lens rotating shafts and an axis of an abrasive wheel shaft of a grinding abrasive wheel on the basis of processing data while rotating the lens, thereby grinding the lens in pressure contact with the abrasive wheel. The apparatus of this type has a processing-completion detecting mechanism for detecting whether or not the entire periphery of the lens has been processed in accordance with processing data. In general, the mechanism is designed to detect, through a mechanical contact or using a sensor, whether the axis-to-axis distance between the lens rotating shafts and the abrasive wheel shaft has reached a predetermined distance based on the processing data. 
     In the case where the lens chucked by the two lens rotating shafts is processed by being brought into pressure contact with the abrasive wheel, the lens rotating shafts are slightly deflected due to their rigidity in a direction in which the lens rotating shafts escape from the abrasive wheel. The lens is clamped through a suction cup; however, if the rigidity of the suction cup portion is weak, the lens is also slightly deflected in the direction in which it escapes from the abrasive wheel. For this reason, the above-described processing-completion detecting mechanism determines the completion of processing at a stage where the actually ground lens is slightly larger than the intended size. This hinders the accurate processing. 
     As a conventional countermeasure against this problem, even after the completion of processing is detected, the lens is rotated idly until the deflection or distortion is overcome, to ensure that unprocessed portions will be processed. 
     However, if the number of idle rotations after detection of the completion of processing is set for the purpose of grinding all the lenses with high accuracy and such setting is made on the basis of thick lenses which are difficult to process, then excessive idle rotation (and thus wasteful processing time) is caused in the case of thin lenses even though the thin lenses have been already processed without any unprocessed portions. Conversely, if the setting of the number of idle rotations is insufficient (small), thick lenses cannot be processed with high accuracy. 
     SUMMARY OF THE INVENTION 
     In view of the above-described problems, it is an object of the present invention to provide an eyeglass lens grinding apparatus, which can accurately detect the completion of processing without any excessive idle rotation, thereby making it possible to perform high-accuracy processing. 
     To attain the above object, the present invention is characterized by having the following features. 
     (1) An eyeglass lens grinding apparatus for grinding a periphery of a lens to be processed, the apparatus comprising: 
     lens rotating means, having a lens rotation shaft, for holding and rotating the lens; 
     abrasive wheel rotating means, having an abrasive wheel rotation shaft, for rotating a lens grinding abrasive wheel; 
     axis-to-axis distance varying means for varying a distance between an axis of the lens rotation shaft and an axis of the abrasive wheel rotation shaft so that the lens is brought into pressure contact with the abrasive wheel for processing; 
     detecting means for detecting a state of rotation of the lens or the abrasive wheel; 
     judging means for judging whether the lens has been completely processed, based on a result of detection by the detecting means. 
     (2) The eyeglass lens grinding apparatus according to (1), wherein the detecting means detects a rotational torque of the lens or a rotational torque of the abrasive wheel. 
     (3) The eyeglass lens grinding apparatus according to (2), wherein the judging means judges whether the lens has been completely processed, based on a comparison in which the rotational torque detected by the detecting means is compared with a certain rotational torque. 
     (4) The eyeglass lens grinding apparatus according to (1), wherein: 
     the lens rotating means includes a lens rotating motor for rotating the lens rotation shaft; 
     the abrasive wheel rotating means includes an abrasive wheel rotating motor for rotating the abrasive wheel shaft; and 
     the detecting means detects a rotational torque of said lens rotating motor or a rotational torque of said abrasive wheel rotating motor. 
     (5) The eyeglass lens grinding apparatus according to (4), wherein the detecting means detects an electric current supplied to the lens rotating motor or an electric current supplied to the abrasive wheel rotating motor to obtain the rotational torque. 
     (6). The eyeglass lens grinding apparatus according to (4), wherein the judging means judges whether the lens have been completely processed, based on a comparison in which the rotational torque detected by the detecting means is compared with a certain rotational torque. 
     (7) The eyeglass lens grinding apparatus according to (1), wherein the detecting means detects a rotational speed of the abrasive wheel or the abrasive wheel rotating shaft. 
     (8) The eyeglass lens grinding apparatus according to (1), wherein: 
     the abrasive wheel rotating means includes an abrasive wheel rotating motor, and a transmission member for transmitting a rotational torque of the motor to the abrasive wheel rotating shaft; and 
     the detecting means detects a rotational speed of the transmission member. 
     (9) The eyeglass lens grinding apparatus according to (1), further comprising: 
     input means for inputting data on a shape of an eyeglass frame to which the lens is to be fitted, and data on a layout of the lens with respect to the eyeglass frame; 
     arithmetic means for obtaining lens processing data based on the data thus inputted; and 
     control means for controlling operation of the axis-to-axis distance changing means based on the processing data thus obtained. 
     (10) The eyeglass lens grinding apparatus according to (1), further comprising: 
     control means for controlling operation of the axis-to-axis distance changing means based on a result of judgement by the judging means. 
     (11) An eyeglass lens grinding apparatus for grinding a periphery of a lens to be processed, the apparatus comprising: 
     a lens rotation shaft which holds and rotates the lens; 
     a lens rotating device having a lens rotating motor and a first transmission member which transmits a rotational torque of the lens rotating motor to the lens rotation shaft; 
     an abrasive wheel rotation shaft which rotates a lens grinding abrasive wheel; 
     an abrasive wheel rotating device having an abrasive wheel rotating motor and a second transmission member which transmits a rotational torque of the abrasive wheel rotating motor to the abrasive wheel rotation shaft; 
     a moving device which causes a relative movement between the lens rotation shaft and the abrasive wheel rotation shaft to vary an axis-to-axis distance between the lens rotation shaft and the abrasive wheel rotation shaft, thereby brining the lens into pressure contact with the abrasive wheel for processing; 
     a detector which detects a state of rotation of the lens or the abrasive wheel; and 
     a controller which judges whether the lens has been completely processed, based on a result of detection by the detector. 
     (12) The eyeglass lens grinding apparatus according to (11), wherein the detector detects the rotational torque of the lens rotating motor or the rotational torque of the abrasive wheel rotating motor. 
     (13) The eyeglass lens grinding apparatus according to (12), wherein the detector detects an electric current supplied to the lens rotating motor or an electric current supplied to the abrasive wheel rotating motor to obtain the rotational torque. 
     (14) The eyeglass lens grinding apparatus according to (12), wherein the controller judges whether the lens has been completely processed, based on a comparison in which the rotational torque detected by the detector is compared with a certain rotational torque. 
     (15) The eyeglass lens grinding apparatus according to (11), wherein the detector detects a rotational speed of the abrasive wheel, the abrasive wheel rotation shaft or the second transmission member. 
     (16) The eyeglass lens grinding apparatus according to (11), further comprising: 
     an input device which inputs data on a shape of an eyeglass frame to which the lens is to be fitted, and data on a layout of the lens with respect to the eyeglass frame; and 
     wherein the controller obtains lens processing data based on the data thus inputted, and controls operation of the moving device based on the processing data thus obtained. 
     (17) The eyeglass lens grinding apparatus according to (11), wherein the controller controls operation of the moving device based on the a result of judgment. 
     The present disclosure relates to the subject matter contained in Japanese patent application No. Hei. 10-184128 (filed on Jun. 30, 1998), which is expressly incorporated herein by reference in its entirety. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a perspective view illustrating an overall configuration of an eyeglass lens grinding apparatus in accordance with the present invention; 
     FIG. 2 is a schematic diagram illustrating the construction of an abrasive-wheel rotating section and a carriage section; 
     FIG. 3 is a diagram illustrating a lens chuck mechanism; 
     FIG. 4 is a block diagram of essential portions of a control system for the overall apparatus; and 
     FIG. 5 is a diagram for explaining an example in which the number of rotations of an abrasive-wheel rotating shaft is detected. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the accompanying drawings, a description will be given of an embodiment of the present invention. FIG. 1 is a perspective view illustrating an overall configuration of an eyeglass lens grinding apparatus in accordance with the present invention. Arranged on a body base  1  are an abrasive-wheel rotating section  2  for rotating an abrasive wheel group  20 , a carriage section  3  for bringing the subject lens clamped by two lens chuck shafts into pressure contact with the abrasive wheel group  20 , and a lens-shape measuring section  4 . An eyeglass-frame measuring section  5  is incorporated in an upper rear portion of the apparatus, and a display section  6  for displaying results of measurement and processing information as well as an input section  7  having various input switches are arranged on the front surface side of the apparatus casing. 
     Next, a description-will be given of the construction of the major sections with reference to FIGS. 1 to  4 . FIG. 2 is a schematic diagram illustrating the construction of the abrasive-wheel rotating section  2  and the carriage section  3 . FIG. 3 is a diagram illustrating a lens chuck mechanism. FIG. 4 is a block diagram showing major components of a control system for the overall apparatus. 
     Abrasive-wheel Rotating Section 
     The abrasive wheel group  20  includes a rough abrasive wheel  20   a  for glass lenses, a rough abrasive wheel  20   b  for plastic lenses, and a finishing abrasive wheel  20   c  for beveling and plano-processing, and its abrasive-wheel rotating shaft  21  is rotatably held by a spindle unit  22  secured to the base  1 . A pulley  23  is attached to an end of the abrasive-wheel rotating shaft  21 , and the pulley  23  is linked to a pulley  25  attached to a rotating shaft of an DC motor  26  for the rotation of the abrasive wheel through a belt  24 . Consequently, the abrasive wheel group  20  is rotated as the motor  26  is rotated. 
     Carriage Section 
     A substantially H-shaped carriage  300  is arranged to chuck and rotate a subject lens (a lens to be processed) L using two lens chuck shafts  302 L and  302 R. The carriage  300  is rotatable and slidable with respect to a shaft  350  secured to the base  1  and extending in parallel to the abrasive-wheel rotating shaft  21 . Hereafter, a description will be given of a lens chuck mechanism, a lens rotating mechanism, a mechanism for moving the carriage  300  along an X-axis and a mechanism for moving the carriage  300  along a Y-axis, by assuming that the direction in which the carriage  300  is moved in parallel to the abrasive-wheel rotating shaft  21  is the X-axis, and that the direction in which the shaft-to-shaft distance between the lens chuck shafts ( 302 L,  302 R) and the abrasive-wheel rotating shaft  21  is changed by the rotation of the carriage  300  is the Y-axis. 
     (a) Lens Chuck Mechanism 
     As shown in FIG. 3, the left chuck shaft  302 L and the right chuck shaft  302 R are held rotatably and coaxially by a left arm  301 L and a right arm  301 R of the carriage  300 , respectively. The left chuck shaft  302  is provided with a cup receiver  303  to receive a suction cup  50  aligned and fixed to the lens L, whereas the right chuck shaft  302 R is provided with a lens pushing member  321  for depressing the lens L. 
     A feed screw  310  is rotatably held inside the right arm  301 R and located at the rear of the right chuck shaft  302 R. A pulley  312  is attached to the shaft of a chuck motor  311  secured to the center of the carriage  300 . The rotation of the pulley  312  is transmitted to the feed screw  310  through a belt  313 . A feed nut  315  is disposed inside the feed screw  310  to threadingly engage the feed screw  310 . The rotation of the feed nut  315  is regulated by a key way  318  formed in a screw guide  317 , so that the rotation of the feed screw  310  causes the feed nut  315  to be moved in the chuck shaft direction (i.e. in the X-axis direction). A cup ring  320  is attached to a tip of the feed nut  315  for rotatably connecting the right chuck shaft  302 R thereto. Therefore, the right chuck shaft  302 R is rotatable, and is moved in the axial direction of the chuck shaft by the feed nut  315 . The lens pushing member or lens holder  321  attached to a distal end of the right chuck shaft  302 R presses the lens L to chuck the lens in cooperation with the left chuck shaft  302 L. The chuck pressure at this time is detected as an electric current flowing across the motor  311 , and the chuck pressure is controlled by supplying a current corresponding to a necessary chuck pressure. A current detector  120  detects the electric current flowing across the motor  311 , and supplies a detection signal through a signal processing section  121  to a control section  100 . 
     The right chuck shaft  302 R is slidably fitted into a pulley  330  rotatably held by bearings. The right chuck shaft  302 R is designed to transmit its rotating force to the pulley  330 . 
     (b) Lens Rotating Mechanism 
     A pulley  340  is attached to the left chuck shaft  302 L. This pulley  340  is linked to a pulley  343  of a drive motor  342  which is secured to the rear side of the carriage left arm  301 L through a belt  341 . When the motor  342  rotates, the left chuck shaft  302 L is rotated, and the rotating force of the left chuck shaft  302 L is transmitted to the chucked lens L through the cup receiver  303  and the suction cup  50 , thereby rotating the lens L. During chucking, since the right chuck shaft  302 R is pressed against the lens L through the lens holder  321  as described above, the right chuck shaft  302 R is rotated in accordance with and in synchronism with the angle of rotation of the lens L. The rotation of the right chuck shaft  302 R is transmitted to an encoder  333 , which is attached to the rear of the right arm  301 R, through the pulley  330 , a belt  331 , and a pulley  332 , so that the encoder  333  detects the angle of rotation of the right chuck shaft  302 R. 
     In addition, the right chuck shaft  302 R may be mechanically coupled so that the right chuck shaft  302 R is rotated in synchronism with the left chuck shaft  302 L by the rotation of the motor  342 . 
     (c) Mechanism for Moving the Carriage in the X-Axis Direction 
     A lower central section of the carriage  300  is held by the bearings  351  and  352  rotatably and slidably with respect to the shaft  350  secured to the base  1 , and an intermediate plate  360  is rotatably secured to an end portion of the left-side bearing  351 . Two cam followers  361  are attached to a rear end of the intermediate plate  360  at a lower portion thereof, and these cam followers  361  nip a guide shaft  362  fixed to the base  1  in parallel positional relation to the shaft  350 . Consequently, the carriage  300  can be moved in the lateral direction (X-axis direction) together with the intermediate plate  360  while being guided by the shaft  350  and the guide shaft  362 . This movement is effected by a pulse motor  363  for the X-axis movement, which is secured to the base  1 . A belt  366  is suspended between a pulley  364  attached to the rotating shaft of the motor  363  and a pulley  365  rotatably supported by the base  1 . A linking member  367  for linking the belt  366  and the intermediate plate  360  is secured to the belt  366 . 
     (d) Mechanism for Moving the Carriage in the Y-Axis Direction 
     A servo motor  370  for the Y-axis movement is fixed to the intermediate plat  360  to rotate the carriage  300  about the shaft  350 . The motor  370  has an encoder  371  for detecting the angle of rotation. A gear  372  is attached to the rotating shaft of the motor  370 , and the gear  372  meshes with a gear  373  fixed to the bearing  351 . Accordingly, the carriage  300  can be rotated about the shaft  350  as the motor  370  is rotatingly driven, thereby making it possible to control the Y-axis movement, i.e. the shaft-to-shaft distance between the abrasive-wheel rotating shaft  21  and the lens chuck shafts (the chuck shafts  302 L and  302 R). The encoder  371  detects the amount of movement of the carriage  300  in the Y-axis direction on the basis of the angle of rotation by the motor  370 . Since the rotational torque of the motor  370  is detected by an electric current detector  124  and a signal processing section  125 , the control section  100  controls the rotational torque of the motor  370  through electric power supplied to the motor  370 , to thereby prevent an excessive processing pressure applied to the lens L. 
     A sensor plate  375  is provided in the rear of the left arm  301 L of the carriage  300 , and as its position is detected by a sensor  376  fixed to the intermediate plate  360 , the position of the original point of the rotation of the carriage  300  can be ascertained. 
     Next, a description will be given of the operation of the apparatus. First, the shape of an eyeglass frame to which a lens is to be fitted is measured by the eyeglass-frame measuring section  5 . If a NEXT DATA switch  701  of the input section  7  is pressed, the measured data is stored in a data memory  101 , and a target lens shape F is simultaneously displayed on a display of the display section  6 . The operator inputs layout data, such as the PD value of the wearer, the FPD value of the eyeglass frame, and the optical center height, by operating the switches of the input section  7 . The operator also enters processing conditions including the material of the lens, the material of the frame, and the processing mode, and the like. Upon completion of the entry of the processing conditions, the operator operates a switch  702  to chuck the lens L by driving the motor  311  through a driver  110 , and then the operator presses a START switch  703  to start processing. The control section  100  sequentially performs the lens shape measurement and the designated processing in accordance with a processing sequence program on the basis of the inputted data, processing conditions, and the like. 
     The control section  100  obtains processing radius vector information on the basis of the inputted target lens shape data and layout data (refer to U.S. Pat. No. 5,347,762). Subsequently, the control section  100  measures the shape of the lens L using the lens-shape measuring section  4 , and determines whether the lens L can be processed into the target lens shape. The control section  100  drives the motor  342  for lens rotation, the motor  370  for Y-axis movement and the motor  363  for X-axis movement through drivers  111 ,  113  and  112 , to thereby move the lens L to a measuring position. Subsequently, the lens-shape measuring section  4  is operated to obtain shape information based on the processing radius vector information (the construction of the lens-shape measuring section  4  and the measuring operation are basically similar to those described in U.S. Pat. No. 5,347,762). Upon completion of the lens shape measurement, grinding is performed in accordance with the designated processing mode. First, processing starts with rough grinding. The control section  100  moves the carriage  300  using the motor  363  so that the lens L is located above the rough abrasive wheel  20   a  for glass lenses or the rough abrasive wheel  20   b  for plastic lenses depending on the designated lens material. Subsequently, in accordance with rough processing data obtained from the processing radius vector information, the movement of the carriage  300  in the Y-axis direction is controlled in association with the rotational angle of the lens L being rotated, whereby the rough grinding is performed with the lens L being brought into pressure contact with the rough abrasive wheel. The rotational angle of the lens L is detected by the encoder  333 , and the amount of the movement of the carriage  300  in the Y-axis direction in association with the rotational angle is detected by the encoder  371 . The control section  100  uses these detected values to manage the processed shape of the lens L. 
     In this manner, the control section  100  moves the carriage  300  in accordance with the processing data, and grinds the lens L by bringing it into pressure contact with the abrasive wheel. During the grinding of the lens L, the chuck shafts are slightly deflected in a direction in which they escape from the abrasive wheel. In a case where the rigidity of the rubber portion of the suction cup  50  is weak, the lens L itself is also slightly distorted in the direction in which it escapes from the abrasive wheel. However, after the carriage  300  is moved to the position of processing completion based on the processing data, the lens L is ground by the abrasive wheel while such deflection and distortion are gradually reduced. 
     A larger torque (load) acts on the rotation of the abrasive wheel grinding the lens L than the abrasive wheel not grinding the lens L. As the processing is closer to the stage of the completion of processing, the abrasive wheel and the lens are in a state in which they slightly abut against each other, and at the stage of the completion of processing, the abrasive wheel rotates idly. Therefore, when the rotational torque of the abrasive wheel becomes less than or equal to the rotational torque of the abrasive wheel in the idle rotation, it can be judged that the processing of the lens L has been completed. The rotational torque of the abrasive wheel can be known from the electric current flowing across the motor  26 . The current flowing across the motor  26  is detected by the current detector  126 , and the detection signal is subjected to signal amplification and A/D conversion by the signal processing section  127  and then inputted to the control section  100 . The control section  100  ascertains the state of rotational torque of the motor  26  on the basis of the inputted signal, and determines that the processing of the lens L has been completed if the rotational torque has reached a predetermined level or below. 
     In addition, the determination of the processing completion can also be carried out by monitoring the rotational torque applied to the lens L (lens chuck shaft) being ground by the rotating abrasive wheel. During the processing of the lens L, the driving of the motor  342  for rotating the lens chuck shaft is controlled so that the processing is carried out at a predetermined rotating position on the basis of processing data based on processing radius vector information as well as the angle of rotation detected by the encoder  333 . The rotational load applied to the lens L by the abrasive wheel rotated at high speed causes the lens chuck shaft to be slightly rotated. This rotation is detected by the encoder  333 , and the control circuit  100  drives the motor  342  so as to return the lens chuck shaft to a predetermined rotating position. At this time, a larger rotating torque is applied to the motor  342  than when the lens L is not being ground (i.e., when the abrasive wheel is in the idle rotation). Accordingly, by monitoring the current flowing across the motor  342  through the current detector  122  and the signal processing unit  123 , in the same way as in the detection of the rotational torque of the abrasive wheel, the processing completion can be determined when the rotational torque applied to the lens L has been reached a predetermined level in which the abrasive wheel is in the idle rotation. 
     As described above, the determination for the processing completion on the basis of the state of the rotational torque of the abrasive wheel or the lens chuck shaft makes the processing accurate, and the processing completion can be determined at an appropriate timing irrespective of the thickness or the hardness of the lens L. This determination for the processing completion is similarly applied to the finish grinding using the finishing abrasive wheel  20   c.    
     In addition, in the case where the processing completion is determined on the basis of the state of rotation of the abrasive wheel rotated at high speed, the state of the rotational load can be recognized not by monitoring the rotational torque but from the number of rotations (rotating speed) of the abrasive wheel, the abrasive-wheel rotating shaft or its rotation transmitting member if an element, such as a DC motor, is used whose number of rotations changes in accordance with a predetermined relationship to the rotational load. For example, as shown in FIG. 5, the number of rotations may be detected as follows: The detecting light is projected from a LED  601  onto the pulley  23  fixed to the abrasive-wheel rotating shaft  21 , and a photosensor  602  receives the reflecting light from a detection mark  600  provided on the rotating shaft  21 . On the basis of the state of the reception of the reflected light, the number of the rotations is detected. 
     As described above, in accordance with the present invention, since the completion of processing can be determined appropriately with high accuracy, highly efficient processing can be performed. In addition, it is possible to perform high-accuracy processing since the accuracy in the determination of the completion of processing is improved.