LENS GRINDING APPARATUS

Abstract: There is disclosed a lens grinding apparatus having a lens rotating shaft (15) on which a lens to be ground is mounted and a grinding wheel (21) for grinding the lens. The invention is characterized in that the lens grinding apparatus comprises outer diameter measuring means (17) for measuring the outer diameter of the grinding wheel, arithmetic means for calculating a wearout quantity of the grinding wheel based on a measurement made by the measuring means, adjusting means (24) for adjusting an intershaft distance between the lens rotating shaft and a grinding wheel rotating shaft, and control means for controlling the adjusting means based on the wearout quantity and performing a wearout correction.

Description: This invention relates to a lens grinding apparatus. In a lens edging or bevelling machine used as a lens grinding apparatus, there are two kinds of tools : one is a coarse grinding tool or coarse grinding wheel having a large grinder grain size and the other is a finish grinding tool or finish grinding wheel having a fine grinder grain size. According to such conventional lens grinding apparatuses, a lens is roughly ground by the coarse grinding wheel copying a template and, thereafter, is subjected to a V-edging or V-bevelling treatment using the finish grinding tool. A lens edging machine according to the prior art portion of claim 1 is disclosed, for instance, in EP-A-0 143 468. Because of the foregoing reason, since the grinding quantity of stock removal using the coarse grinding wheel is much larger than that of the finish grinding wheel, the wearout quantity of the coarse grinding wheel becomes larger than that of the finish grinding wheel. Because of the foregoing reason, when such grinding wheels are used for a long time, the grinding quantity of the finish grinding wheel is increased, thereby to necessitate a longer working time. In view of the above, the conventional lens edging or bevelling machine are provided with a mechanism for manually adjusting the height of a template receiver for each grinding wheel in order to correct the wearout quantity (hereinafter simply referred to as wearout-correction) of the above-mentioned grinding wheels. In general, an operator of the grinding wheels has a difficulty in finding the changes of working state due to the difference in wearout quantities of the grinding wheel. Because of the foregoing reason, it is an actual practice that the wearout-correction is not performed on the grinding wheels, but the lens worked is measured in diameter to merely correct the finish size. In this way, the lens was often worked in an incorrect state. When the grinding is performed in the foregoing state, since the coarse grinding wheel is more rapidly worn than the finish grinding wheel, the difference of diameter between the coarse grinding wheel and the finish grinding wheel becomes larger and, therefore, the quantity ground by the finish grinding wheel becomes larger, which invites the drawbacks in that the grinding time is increased and the finish grinding wheel, which is more expensive, is worn out more quickly. Further, when the wearout-correction is performed, it is difficult for the operator of the grinding wheel to effect the correction directly and it is a usual practice that a service man who is an expert in this field chiefly takes care of it. The present invention was accomplished in order to eliminate the afore-mentioned drawbacks of the prior art. SUMMARY OF THE INVENTION It is therefore the object of the present invention to provide a lens grinding apparatus, wherein the outer diameter of a grinding wheel is automatically measured with a simple constitution and, based on the measurement, the wearout-correction of the grinding wheel is performed during grinding operation. EP-A-0 131 743 describes a gauge for measuring the wearout quantity of a grindstone, but which is somewhat complicated. In order to achieve the above object, there is essentially provided a lens grinding apparatus according to claim 1 and a method for obtaining a wearout quantity of a grinding wheel of a lens apparatus according to claim 4. With the above-described constitution of the present invention, when the positions of the periphery of the grinding wheel, etc. are measured by the outer diameter measuring means, the outer diameter of the grinding wheel and the wearout quantity are computed by the arithmetic means from the measured value of the outer diameter measuring means. And, the adjusting means are controlled based on the wearout quantity of the grinding wheel to adjust the intershaft distance between the lens rotating shaft and the grinding wheel at the final grinding position of the lens to be ground. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawings, wherein: Figs. 1 through 7 show one embodiment of the present invention, in which; Fig. 1 is a perspective view, partly omitted, of a lens edging or bevelling machine (lens grinding apparatus); Fig. 2 is a front view of the reference template of Fig. 1; Fig. 3 is a side view of Fig. 2; Fig. 4 is a front view of the lens to be ground of Fig. 1; Fig. 5 is a left side view of Fig. 4; Fig. 6 is an electric circuit of the lens edging or bevelling machine of Fig. 1; Figs. 7(A), 7(B) and 7(C) are flow charts of the lens edging or bevelling machine of Fig. 1. DETAILED DESCRIPTION OF THE EMBODIMENTS One preferred embodiment of the present invention will be described hereinafter with reference to the accompanying drawings. Figs. 1 through 7 illustrate one embodiment of the present invention. Fig. 1 illustrate a perspective view, partly cut out, of a lens edging or bevelling machine as a lens grinding apparatus. In Fig. 1, 1 denotes a housing-like main body opened up upwardly of a lens edging or bevelling machine, 2 denotes a rear wall of the main body 1, and 3 denotes a bottom wall of the main body 1. The rear wall 2 is integrally provided at its generally central portion with bearing projections 4, 4 projecting upwardly therefrom. On upper portions of the bearing projections 4, 4, a carriage revolving shaft 5 is rotatably and movably held through a bearing 6 for movement in the axial direction. On both ends of the carriage revolving shaft 5, rear side pieces 7a, 7b projecting from both sides of the rear end of the carriage 7 are fixed. At both side portions of the rear wall 2, pulley shafts 8, 9 extending upwardly are fixed. On upper end portions of the pulley shafts 8, 9, pulleys 10, 11 are rotatably held. On the rear wall 2, a cross feed motor 12 disposed adjacent to the pulley shaft 8 is fixed. On an output shaft 12a of the cross feed motor 12 extending upwardly, a drive pulley 13 is fixed. And, on the rear side pieces 7a, 7b of the carriage 7, both end portions of a wire 14 looped around the pulleys 10, 11 and the drive pulley 13 are fixed. As the cross feed motor 12, a pulse motor is used. At both sides of a free end portion of the carriage 7, projecting portions 7c, 7d for holding the shaft are integrally provided. On the projecting portion 7c, a lens rotating shaft 15A parallel with the carriage revolving shaft 5 is revolvably and longitudinally unmovably held. While, on the other projecting portion 7d, a lens rotating shaft 15B having an axial line in alignment with the lens rotating shaft 15A is rotatably and movably held for movement in the axial direction. In the figure, 16 denotes a handle adapted to adjust the movement of the lens rotating shaft 15B in the axial direction, and 17 denotes a reference circular plate made of metal or hard plastic and held between the lens rotating shafts 15A, 15B. The reference circular plate 17 is provided with a V-block portion 17a having the same angle as a V-groove of a V-edge grinding wheel 23 (finish grinding wheel) on its periphery and a mounting seat 17b at its center (see Figs. 4 and 5). 18 denotes a reference template detachably attached to an outer end portion of the lens shaft 15A. The reference template 18 has the same diameter as that of the reference circular plate 17 (see Figs. 2 and 3). The lens rotating shafts 15A, 15B are rotated by a motor (not shown). Under the free end portion of the carriage 7, a bracket 19 projecting from the bottom wall 3 of the main body 1 is provided. On the upper end portion of the bracket 19, a grinder shaft 20 parallel with the lens rotating shafts 15A, 15B is rotatably held. On the grinder shaft 20, a grinding wheel 21 is detachably fixed. The grinding wheel 21 comprises a coarse grinding wheel 22 and a V-edge grinding wheel 23. Under the reference template 18, a template receiver 24, a template receiver lifting motor 25 and a power transmission mechanism 26 are provided. The template receiver 24 comprises a pedestal 27, a movable type template receiving piece 28 provided on the pedestal 27, a pivot shaft 29 pivotally supporting the movable type template receiving piece 28 on the pedestal 27 so that the movable type template receiving piece 28 can pivot up and down, and a spring 30 for energizing the movable type template receiving piece 28 upwardly. The movable type template receiving piece 28 is formed in an arcuate shape in its side view, and the curvature of its upper surface 28a is the same as the curvature of the outer periphery of the grinding wheel 21. On the pedestal 27, a microswitch 31 as an outer diameter measuring means is fixed. The template receiver lifting motor 25 is fixed on the bottom wall 3 of the main body 1. As the template receiver lifting motor 25, a pulse motor is used. The power transmission mechanism 26 includes a pinion 32 fixed to the output shaft of the template receiver lifting motor 25, a gear 33 meshed with the pinion 32 and rotatably supported by the bottom wall 3 through a template receiver supporting table (not shown), and a feed screw 34 threadedly engaged with the center of the gear 33 for reciprocal movement and fixed to the under surface of the pedestal 27. Between the pedestal 27 and the template receiver supporting table (not shown), a guide means adapted to vertically guide the pedestal 27 while preventing the horizontal pivot of the pedestal 27 is provided. Next, an electric circuit of the V-edging or bevelling machine will be described with reference to Fig. 6. In Fig. 6, the arithmetic control circuit 35 is inputted with an on-off signal from the microswitch 31 through a NOT circuit (inverter) 36 and also with on-off signals from a correct quantity input switch 37 and a correction start switch 38. The arithmetic control circuit 35 is adapted to control the generation and stop generation of pulse of a pulse generator 39 and change over a change-over switch 40 to any one of the positions at the normal rotation side/neutral position/reverse rotation side, so that the pulse outputted from the pulse generator 39 is inputted into the template receiver lifting motor 25 through the change-over switch 40, while the pulse outputted from the pulse generator 39 is inputted into the cross feed motor 12 through the change-over switch 41. Moreover, the pulse outputted from the pulse generator 39 is inputted into a resettable counter 42 by the arithmetic control circuit 35, and the pulse quantity counted by the counter 42 is inputted into the arithmetic control circuit 35. The arithmetic control circuit 35 is adapted to input the pulse quantity counted by the counter 42, when the template receiver lifting motor 25 is at work, into a template receiver lifting data memory 44 and to calculate the respective wearout quantities of the coarse grinding wheel 22 and the V-edge grinding wheel 23 based on the data inputted, and then to input the calculated results into a wearout-correction data memory 43. And, when the wearout quantity of the grinding wheel 21 becomes a predetermined value and more, the arithmetic control circuit 35 actuates an indicator 45 to inform the time for exchanging the grinding wheel 21. Moreover, the arithmetic control circuit 35 is adapted to calculate the cross feed quantity of the cross feed motor 12 according to the input from the correction quantity input switch 37 and input the calculated results into a cross feed data memory 46. On the other hand, the arithmetic control circuit 35 is adapted to read a lifting data from the wearout-correction data memory 43 to control the pulse number to be inputted into the template receiver lifting motor 25 and also the read data from the cross feed data memory 46 to control the pulse number to be inputted into the cross feed motor 12. Such calculation and control are progressed in the order shown in the flow charts of Figs. 7(A), 7(B) and 7(C) according to memory memorized in a program memory 47. The carriage 7 is held in the initial position by a carriage lifting position supporting apparatus (not shown) known per se, and an operator mounts the reference circular plate 17 and the reference template 18 on the lens rotating shafts 15A, 15B in the Step S₁. In usual grinding, a lens to be ground is ground at the center of a grinding surface of a coarse grinding wheel. However, in general, since the coarse grinding wheel 22 is wide enough compared with the lens to be ground, the portion excluding the center of the grinding surface is hardly worn. Therefore, the operator properly changes the position from where the lens to be ground is dropped on the grinding surface of the coarse grinding wheel 22 (i.e., correction) so that the grinding surface is evenly worn out, thereby to prolong the service life of the coarse grinding wheel 22. Accordingly, in the Step S₂, in order to designate a position of the grinding surface of the coarse grinding wheel 22 which is to be measured in outer diameter, the operator inputs this correct quantity into the arithmetic control circuit 35 through the correct quantity input switch 37 on a key board. Due to the foregoing, the arithmetic control circuit 35 allows the cross feed data memory 46 to memorize the correct quantity as carriage feed quantity data. Next, in the Step S₃, when the correction start switch 38 is turned on, the arithmetic control circuit 35 changes over the change-over switch 40 to the normal rotation side and, at the same time, actuates the pulse generator 39, then causes the template receiver lifting motor 25 to rotate normally, then causes the template receiver 24 to move upwardly, then causes the template receiving surface 28a to abut against the reference template 18 and then turns the microswitch 31 on. The "on" signal from the microswitch 31 causes the output of the inverter 36 to the arithmetic control circuit 35 to become low level. Receiving the low level state of the inverter 36, the arithmetic control circuit 35 changes over the change-over switch 40 to the neutral position and, at the same time, stops the generation of the pulse from the pulse generator 39. Furthermore, it cancels the carriage support of the carriage lifting position supporting apparatus (not shown) known per se. Then, in the Step S₄, the arithmetic control circuit 35 changes over the change-over switch 41 to the normal rotation side and, at the same time, actuates the pulse generator 39 and counter 42. Due to the foregoing, the cross feed motor 12 is rotated normally to cause the carriage 7 to move laterally. When the arithmetic control circuit 35 interprets that the count value of the counter 42 reached the predetermined cross feed quantity, i.e., the quantity for which the reference circular plate 17 is positioned at an upper part of the center of the grinding surface of the coarse grinding wheel 22, it causes the change-over switch 41 to return to its neutral position and, at the same time, causes the pulse generator 39 to stop and resets the counter 42. Due to the foregoing, the reference circular plate 17 is positioned at the upper part of the coarse grinding wheel 22. Then, in the Step S₅, the arithmetic control circuit 35 interprets whether the measurement on the outer diameter of the coarse grinding wheel has been completed or not. When the measurement is interpreted as completed, it goes to the following Step S′₆. Since the measurement is not completed in this description of the operation, it moves to the following Step ₆ in which the arithmetic control circuit 35 interprets whether the correction is necessary or not depending on whether the data are memorized in the cross feed data memory 46 or not and, when necessary, it goes to the following Step S₇ but, when unnecessary, it goes to the Step S₉. When the cross correction is interpreted as necessary in the preceding Step S₆, the arithmetic control circuit 35 changes over the change-over switch 41 to the normal rotation side or reverse rotation side according to the memory of the program memory 47 and causes the pulse generator 39 to generate a pulse to rotate the cross feed motor 12 normally or reveresly. Due to the foregoing, the output of rotation of the cross feed motor 12 is transmitted to the wire 14 through the output shaft 12a and drive pulley 13 and the carriage 7 is moved toward the pulley 11 or 10 of Fig. 1. In such movement, the counter 42 counts the pulse from the pulse generator 39 and inputs the count quantity into the arithmetic control circuit 35. And, the arithmetic control circuit 35, when the count quantity became the quantity corresponding to the cross feed data of the cross feed data memory 46, stops the generation of pulse from the pulse generator 39 and returns the change-over switch 41 to the neutral position side to stop the actuation of the cross feed motor 12. The cross feed position of the reference circular plate 17 is brought to be in alignment with the outer diameter measuring position on the grinding surface which is to be ground. When the Step S₇ is completed, the arithmetic control circuit 35 causes the pulse generator 39 to generate a pulse according to the memory of the memory program 47 in the Step S₈ and changes over the change-over switch 40 to the reverse rotation side to rotate the template receiver lifting motor 25 reversely. The rotation of the template receiver lifting motor 25 causes the power transmission mechanism 26 to be actuated, the template receiver 24 is moved downwardly, and then the free end portion of the carriage 7 and the reference circular plate 17 held thereon are moved downwardly by a predetermined quantity. In such downward movement, the counter 42 counts the pulse from the pulse generator 39 and inputs the count quantity into the arithmetic control circuit 35. The above-mentioned action is consecutively performed in the Steps S₈, S₉ until the microswitch 31 is turned off. In this way, the free end portion of the carriage 7 and the reference circular plate 17 held thereon are moved downwardly and the reference circular plate 17 is abutted against the periphery of the coarse grinding wheel 22. And, the action of the template receiver 24 is repeated until the reference circular plate 17 is abutted against the coarse grinding wheel 22 and the microswitch 31 is turned off. Moreover, the pulse generated from the pulse generator 39 according to the action of the template receiver lifting motor 25 is counted by the counter 42 and inputted into the arithmetic control circuit 35. And, when the microswitch is turned off, the inverter 36 becomes high level and the arithmetic control circuit 35 makes the change-over switch 40 neutral to stop the rotation of the motor 25 and, at the same time, to stop the generation of a pulse from the pulse generator 39. Then, it goes to the Step ₁₀, in which the arithmetic control circuit 35 calculates the outer diameter of the coarse grinding wheel 22 and the difference between such outer diameter measuring value and a known outer diameter value of an unused coarse grinding wheel as a wearout quantity based on the pulse number from the counter 42 and inputs the wearout quantity into the wearout-correction data memory 43. Thereafter, the arithmetic control circuit 35 interprets whether the wearout quantity of the coarse grinding wheel 22 is within the predetermined value or not (i.e., whether the grinding wheel must be exchanged or not) in the Step ₁₁ and, when the wearout quantity is the predetermined value and more, actuates the indicator 45 to warn the necessity of the exchange of a grinding wheel in the Step S₁₂. On the other hand, when the wearout quantity is within the predetermined value, it goes to the Step ₁₃ in which it is interpreted whether the measurement on the outer diameter of the V-edge grinding wheel 23 is completed or not. And, when not completed, it goes to the Step S₅. After it is interpreted that the measurement on the outer diameter of the coarse grinding wheel is completed in the Step S₅, it goes to the Step S'₆. In the Step S'₆, the change-over switch 41 is changed over to the normal rotation side as in the same procedure in the Step S₄, the cross feed motor 12 is rotated normally, the carriage 7 is moved toward the pulley 11, and the V-edge 17a of the reference circular plate 17 and the V-groove grinding surface of the V-edge grinding wheel 23 are brought to be in alignment with respect to each other. When this action is completed, the control action of the arithmetic control circuit 35 goes to the Step S₆. Then, the procedures of the Steps S₈ to S₁₂ are performed, and the measurement on the outer diameter of the V-edge grinding wheel 23 and the wearout correct value are computed. On the other hand, when the measurement of the V-edge grinding wheel 23 is completed, it goes to the Step S₁₄ in which the change-over switch 40 is changed over to the normal rotation side, the template receiver lifting motor 25 is rotated normally according to the pulse from the pulse generator 39, the cross feed motor 12 is rotated reversely after the template receiver 24 is lifted upwardly by a predetermined quantity, the carriage 7 is moved to its initial position side, the reference template 18 and the reference circular plate 17 to be ground are returned to their initial positions in the Step S₁₅, the carriage supporting apparatus (not shown) known per se is actuated to hold the carriage 7 in the lifted position and, thereafter, the template receiver 24 is moved downwardly to the initial position. By this, the measurement on the outer diameters of the coarse grinding wheel 22 and V-edge grinding wheel 23 and the calculation of the wearout quantity are completed. When the lens is ground, the respective wearout-correction values of the coarse grinding wheel 22 and V-edge grinding wheel 23, which are memorized in the memory of the wearout-correction data memory 43, are added to the predetermined downward movement quantity of the template receiver 24 to move the template receiver 24 downwardly and the known lens grinding action is started in the foregoing state.

Claims: A lens grinding apparatus comprising a lens rotating shaft (15) for holding and rotating a lens to be ground and for mounting a lens template on a one end thereof, a grinding wheel (21) having a rotating shaft (20) for grinding said lens, means for measuring the outer diameter of the grinding wheel (21) independently of or prior to a lens grinding phase performed by said lens grinding apparatus and for adjusting an intershaft distance between the lens rotating shaft and the grinding wheel rotating shaft, arithmetic means (35) for calculating a wearout quantity of the grinding wheel based on a measurement made by said measuring means, characterized in that said measuring and adjusting means further comprise : a reference plate (17) made of metal or hard plastic, comprising a mounting seat (17b) at its center and held by said lens rotating shaft (15) instead of the lens to be ground ; a reference template (18, 47) which is a plate being similar in shape to that of said reference plate (17) and having a diameter which is identical or less than a diameter of said reference plate (17), the reference template (18, 47) being mounted at the one end of the lens rotating shaft instead of a lens template which is mounted when the lens is ground ; a template receiver (24) adapted to come into contact with said reference template (18, 47) and driving means (25, 26) for shifting said template receiver (24) ; and a switch means (31) disposed in said template receiver (24) for sensing whether or not said template receiver (24) comes into contact with said reference template (18, 47) and a counter (42) for counting the displacement value of said template receiver (24) ; the arithmetic means (35) being adapted to calculate the wearout quantity of the grinding wheel (21) based on said displacement value. A lens grinding apparatus as claimed in claim 1, wherein said reference plate (17) is provided on its periphery with a V-block portion (17a) having the same angle as a V-groove of a V-adge grinding wheel (23). A lens grinding apparatus as claimed in claim 1 or 2 further comprising control means (35) for controlling said adjusting means based on the wearout quantity and performing a wearout correction in a lens grinding phase performed thereby. A method for obtaining a wearout quantity of a grinding wheel of a lens grinding apparatus according to any one of claims 1 to 3, comprising steps which include a step for measuring the outer diameter of the grinding wheel (21) and a step for calculating a wearout quantity of the grinding wheel (21) based on a measurement made in said measuring step, characterized in that said steps comprise : a first step for holding said reference plate (17) by said lens rotating shaft (15) instead of the lens to be ground and for mounting on the one end of said lens rotating shaft (15), instead of the lens template, said reference template (18) ; a second step for contacting said reference plate (17) onto the outer diameter of said grinding wheel (21) ; a third step for coming into contact said templace receiver (24) of said adjusting means with said reference template (18) and for counting the displacement value of said template receiver (24) by when said template receiver (24) has been contacted with said reference template (18) ; and a fourth step for calculating the wearout quantity of the grinding wheel (21) based on said displacement value obtained by said third step. A method for obtaining a wearout quantity of a grinding wheel of a lens grinding apparatus as claimed in claim 4 further comprising a fifth step for controlling said adjusting means based on the wearout quantity and for performing a wearout correction in the lens grinding phase performed by said lens grinding apparatus.

Inventors: HATANO, YOSHIYUKI C/O TOKYO KOGAKU KIKAI, ISOKAWA, NOBUHIRO C/O TOKYO KOGAKU KIKAI, SUZUKI, YASUO C/O TOKYO KOGAKU KIKAI
Applicants: KABUSHIKI KAISHA TOPCON
Application year: 1987
Main classification: B24B9
IPC codes: B24B13, B24B49, B24B9