Method and apparatus for measuring the edge thickness of a spectacle lens

Abstract: The V-edge depth of the grinder for grinding the lens and the with of the grinding base are taken into account in the calculation of the all round vector information and the edge thickness of the spectacle lens.

Description: BACKGROUND OF THE INVENTION: Field of the Invention This invention relates to methods for measuring the edge thickness of a spectacle lens. Description of the Prior Art: An example of a conventional method and apparatus for measuring the edge thickness of a lens is in detail described in Japanese Patent Application No. SHO 60-115079 as a component of a lens grinding apparatus disclosed by the same applicant as in the present application. This conventional apparatus for measuring the edge thickness is constituted such that the thickness can be measured based on the lens rim shape of the spectacle frame measured by the frame shape measuring device 10 as shown schematically in Fig. 6. The edge thickness measuring apparatus is shown as a block diagram in Fig. 7. The frame shape measuring apparatus 10 has a symmetric rotator with hexagon-sectional shapes shaped feeler 11 mounted rotatably in the tip. The feeler 11 is connected with a feeler arm 12, which is rotatable about the axis of the perpendicular line As through the edge of contact 11a of the feeler 11, supported by a feeler supporting base 13. And the base 13 is mounted on the rail 14 turned round by a pulse motor 16 and movable by elasticity of a spring 15 fixed to another edge (not shown) of the rail 14. The pulse motor 16 can work by the pulse from a pulse generator 17. When the edge of contact 11a of the feeler 11 is abutted on the V-edge groove Vf, the moving amount ρ i of the feeler 11 is detected by a detector 19 constituted of either an encoder or a position sensor. The detected moving amount ρ i is memorized in a lens rim shape memory 18 together with a supply pulse ϑ i to the pulse motor 16. The moving amount ρ i of the feeler and the rotational amount of the arm, i.e. the radius vector angle ϑ i are memorized as a radius vector information (ρ i , ϑ i ) (i=0,1,2,3...N) of the lens rim F in the lens rim shape memory 18. The moving amount ρ i of the feeler is measured over the V-edge groove all around of the lens rim F. As shown in Fig. 7, the edge thickness measuring apparatus comprises an edge thickness sensor portion 20 and an electric circuit portion 30. The sensor portion 20 includes a lens feeler supporting member 22, which is moved on the guide rail 21 by the driving of a feed screw 26. The screw 26 is rotated by the pulse motor 25. A material lens L is held between lens rotating shafts 28,28 and then the lens L is rotated by the rotation of the shafts 28,28 caused by the driving of the pulse motor 29. The lens feeler supporting member 22 includes lens feelers 23A,23B and detectors 24A,24B. The detectors 24A,24B are constituted of springs 25A,25B for pulling the lens feelers 23A,24B, and encoders or position sensors for detecting the moving amount of the feelers 23A,23B. The pulse based on the length ρ i of the radius vector of the radius vector information (ρ i , ϑ i ) of the lens rim F is supplied into the pulse motor 25, and the feelers 23A,23B moves inside the lens feeler supporting member 22. This movement determines the position of the lens feelers 23A,23B at the point having the length ρ i of the radius vector from the axis of rotation of the lens rotating shafts. The length ρ i of the radius vector is memorized in the lens rim shape memory 18. On the other hand, the pulse based on the rotary angle (radius vector angle) ϑ i is supplied to the pulse motor 29 and then the lens rotating shafts 28,28 are rotated. This rotation of the shafts 28,28 produces the rotation of the material lens L by the rotary angle ϑ i from the reference position. The lens feeler 23A is moved by the elasticity of the spring 25A and then abutted on the front side refraction surface IF of the material lens L. The moving amount f Z i is detected by the detector 24A and memorized in a lens data memory 31. In the same way, the lens feeler 23B is moved by the elasticity of the spring 25B and then abutted on the back side refraction surface LB and the moving amount b Z i is detected by the detector 24B and memorized in a lens data memory 31. This detection is carried out as to all the radius vector informations (ρ i , ϑ i ) (i=0,1,2,3,...N), and the front side refraction surface position information ( f Z i , ϑ i ) and the back side refraction surface position information ( b Z i , ϑ i ) (i=0,1,2,3,...N) on the radius vector shaped locus (ρ i , ϑ i ) of the lens rim are memorized in the lens data memory 31. A first arithmetic circuit 32 of an electric circuit portion 30 mounted in the edge thickness sensor portion 20 calculates the edge thickness information (Δ i , ϑ i ) (i=0,1,2,3,...N) of the lens L on the radius vector shaped locus (ρ i , ϑ i ) based on the front side refraction position information ( f Z i , ϑ i ) and the back side refraction position information ( b Z i , ϑ i ). Furthermore, the maximum edge thickness Δ max and the minimum edge thickness Δ min are counted up from the edge thickness information (Δ i , ϑ i ), and a beveled V-edge (groove) apex position information ( k Z i , ρ i , ϑ i ) (i=0,1,2,3,...N) to form a V-edge in the edge surface of the lens is automatically calculated based on the two values Δ max and Δ min . In the above mentioned way, the lens L is automatically ground. And formed is a configuration that the sectional shape of the lens L is graphically displayed on a display 33. As shown in Fig. 7, the positions of the contact of the lens feelers 23A,23B with the lens L is taken on the tangent line Q through the V-edge apex Y formed in the V-edge grinding of the lens. And the edge thickness Δ i on the tangent line Q is calculated by the first arithmetic circuit 32. The radius of curvature R of the front surface of the lens L is different from that of the back(rear)surface, and the edge thickness of the base B of the edge surface of the lens L to form a V-edge is exactly Δ i ′. Therefore the calculation of the treated V-edge apex position information ( k Z i , ρ i , ϑ i ) not based on the edge thickness Δ i ′ of the base B is inaccurate. And thus, the positions of the lens feelers 23A,23B are moved to those of 23A′ ,23B′ when the edge thickness is measured, as shown in Fig. 8. More detailedly, the positions of the lens feelers 23A,23B on the radius vector locus (ρ i , ϑ i ) is moved to the positions ρ i ′ = ρ i -H where ρ i is the length of the radius vector and H is the depth (or height) of the peripheral ridge, because the V-edge groove bottom YG and the base YB of the V-edge grinder G of a lens grinding apparatus are already known. By this movement, measured is the edge thickness of the base B of the edge surface formed in the lens L at the time when the lens L is ground with the V-edge grinder G. And V-edge apex position information ( k Z i , ρ i , ϑ i ) is calculated based on the edge thickness Δ i ' when the lens is ground with the grinder G. As shown in Fig. 9, however, there is a problem that the V-edge (V-ridge) formed actually on the lens L is an inadequate V-edge in case the edge thickness is smaller than the width (W) of V-edge groove of the grinder G, because the edge surface K of the lens L to grind actually is displaced from the position of the measured edge surface KM owing to the difference between the radius of curvature R f of the front surface of the lens L and the radius of curvature R b of the back surface, in case even if the V-edge apex position information ( k Z i , ρ i , ϑ i ) is obtained based on the edge thickness Δ i ' measured by the above method such that the V-edge apex Y is formed at the point where the edge thickness is divided in the ratio of one to one, for example. Japan patent abstracts vol. 11, No 135 (M-585) [2582], April 28, 1987, and JP-A-61 274 860 (Tokyo Optical Co. Ltd), December 5, 1986, describe a lens shape measuring device and a lens grinding apparatus. On a lens measuring device are provided feelers contacting respectively the front and rear surfaces of a workpiece lens and magnetic encoders for detecting the displacements of the feelers. And movable stages move the feelers along a measure locus on the lens in a predetermined relationship with a supposed edge locus obtained from the shape data of a lens frame of an eye glass frame into which is inserted the lens or the shape data of the lens profiled according to a template. Further, a calculating means provided in the measuring device figures out the edge thickness of lens after mortar working on the basis of the detecting information of the encoders when the feelers are moved on the measured locus. SUMMARY OF THE INVENTION The present invention concerns a method for measuring the edge thickness of a spectacle lens comprising the steps of: inputting an all round radius vector information (ρi, ϑi) of a spectacle frame lens rim for framing said lens (with i=0, 1, 2, 3... N) obtaining an all round measuring radius vector information (ρi', ϑi) by subtracting a V-groove depth (H) of a grinder (G) from the length (ρi) of the radius vector of said all round radius vector information (ρi, ϑi); and obtaining an edge thickness information (Δi, ϑi) corresponding to said all round measuring radius vector information (ρi', ϑ i) by measuring a front side refractive position information (fZi, ϑi) and a back side refractive position information (bZi, ϑi) of said lens corresponding to said measuring radius vector information (ρi', ϑi) in order to obtain an edge thickness information (Δi, ϑi) at the grinding position and a V-edge apex position information (kZi, ρi, ϑi) when the edge of said lens is ground with said grinder (G); characterised by: a first step of comparing a width (W) of a grinding base of said grinder (G) with said measured edge thickness (Δi) and selectively obtaining a partial measuring radius vector information (ρj', ϑj) (j ≦ i) of said lens where a narrower edge thickness (Δj) than said width (W) is measured; a second step of obtaining, by presuming that an edge thickness (Δj') in the position of an again measuring radius vector length (ρj'') of a partial and again measuring radius vector information (pj'', ϑj) (with j≦i) for forming a V-edge of said lens by said V-groove of said grinder (G) in a position corresponding to said partial measuring radius vector information (ρj', ϑj) is approximately equal to said edge thickness (Δj), a measuring radius vector length (ρj'') of said partial measuring radius vector (ρj', ϑj) from said partial measuring radius vector information (ρj'', ϑj) (j ≦ i) as follows: ρj'' = ρj'+dj dj = (1-Δj/W).H (with j ≦ i); and a third step of measuring said front side refractive position information (fZi', ϑi) and said back side refractive position information (bZi', ϑi) of said lens in such a manner as to correspond to said partial and again measuring radius vector information (ρj'', ϑj) which are used for obtaining said V-edge apex position information for grinding the edge of that portion of said lens having said edge thickness (Δj) with said grinder (G). the present invention concerns also a method for measuring the edge thickness of a spectacle lens comprising the steps of: inputting all round radius vector information (ρi, ϑi) of a spectacle frame lens rim for framing the lens (with i=0, 1, 2, 3...N); obtaining all round measuring radius vector information (ρi', ϑi) by subtracting a V-groove depth (H) of a grinder (G) from the length (ρi) of the radius vector of said all round radius vector information (ρi, ϑi); and obtaining an edge thickness information (Δi, ϑi) corresponding to said all round measuring radius vector information (ρi', ϑi) by measuring a front side refractive position information (fZi, ϑi) and a back side refractive position information (bZi, ϑi) of said lens corresponding to said measuring radius vector information (ρi', ϑi) in order to obtain an edge thickness information (Δi, ϑi) in the grinding position and a V-edge apex position information (kZi, ρi, ϑi) when the edge of said lens is ground with said grinder (G); characterised by: a first step of comparing a width (W) of a grinding base of said grinder (G) with an edge thickness (Δi) of said edge thickness information (Δi, ϑi) to obtain partial measuring radius vector information (ρj', ϑj) (with j ≦ i) in which a measured edge thickness (Δj) is less than said width (W) of the grinding base; a second step of obtaining a compensation value t1 according to the following formula: t1 = (1- Δj W )·H on the supposition that, if said measured edge thickness (Δj) less than said width (W) is obtained from j-th partial measuring radius vector information (ρj', ϑj) of a j-th measurement ("-th" is a suffix representing an ordinate number), an edge thickness of j+1-th partial measuring radius vector information (ρj+1', ϑj+1) is defined as (Δj') and, in addition, the edge thickness (Δj') is approximately equal to said measured edge thickness (Δj); a third step of obtaining a compensating radius vector length (τj+1), which corresponds to a length (ρj+1') of the measuring radius vector of said j+1-th partial measuring radius vector information (ρj+1', ϑj+1), according to the following formula: τj+1 = ρj+1'+t1 and obtaining compensating measuring radius vector information (τ j+1, ϑj+1) about said compensating radius vector length (τj+1) and about a radius vector angle (ϑj+1) of said j+1-th partial measuring radius vector information (ρj+1', ϑj+1); a fourth step of measuring an edge thickness (Δj+1) by measuring front and back side refractive position information of said lens according to said compensating measuring radius vector information (τj+1, ϑj+1); a fifth step of comparing said measured edge thickness (Δ j+1) with said preceding measured edge thickness (Δj), and, if said measured edge thickness (Δj+1) is less than said preceding measured edge thickness (Δj), obtaining a compensation value tm according to the following formula: where Δj+m is an edge thickness of measuring radius vector information (ρj+m', ϑj+m) and Δj+m-1 is an edge thickness of measuring radius vector information ( ρj+m-1' , ϑj+m-1 ) precedent to said measuring radius vector information (ρj+m', ϑj+m) (with m=2,3,4,···M,M<N ), the edge thickness (Δj+m) being approximately equal to said edge thickness ( Δj+m-1 ); a sixth step of obtaining a compensating radius vector length (τj+m), which corresponds to a length (ρj+m') of the measuring radius vector of said measuring radius vector information (ρj+m', ϑj+m), according to the following formula: τj+m = ρj+m'+tm and obtaining compensating measuring radius vector information (τ j+m, ϑj+m) about said compensating radius vector length (τj+m) and about a radius vector angle (ϑj+m) of said measuring radius vector information (ρj+m', ϑj+m); and a seventh step of successively measuring front and back side refractive position information of said lens according to said compensating measuring radius vector information (τj+m, ϑj+m). The advantages of the present invention will be well appreciated upon reading of the following description of the invention when taken in conjunction with the attached drawings with understanding that some modifications, variations and changes of the same could be made by the skilled person in the art to which the invention pertains without departing from the scope of claims appended hereto. BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS Fig. 1 is a block diagram showing an embodiment of an edge thickness measuring apparatus according to the present invention; Fig. 2 is a partly diagrammatic sectional view showing a measuring radius vector, a partial re-measuring radius vector, a lens feeler, and a relation between a measured edge thickness and a grinder's shape, each for describing a first embodiment of an edge measuring method according to the present invention; Figs. 3A and 3B are schematic illustrations showing a measuring radius vector, and a relation among the partial re-measuring radius vector and the measured radius vector locus and the partial re-measured radius vector locus, each for explaining the first embodiment of a edge thickness measuring method; Fig. 4 is a schematic illustration showing the measuring radius vector, and a relation among the compensated measuring radius vector and the measured radius vector locus and the compensated measured radius vector locus, each for explaining the second embodiment of an edge thickness measuring method; Fig. 5 is a schematic illustration showing the compensated measured points and the lens feeler at the points, and a relation between the measured edge thickness and the shape of the grinder, each for explaining the second embodiment of an edge thickness measuring method; Fig. 6 is a block diagram showing a constitution of a conventional frame shape measuring apparatus; Fig. 7 is a block diagram showing a constitution of a conventional edge thickness measuring apparatus; Fig. 8 is a schematic illustration showing the measuring radius vector and the lens feeler, and a relation between the measured edge thickness and the shape of the grinder for explaining a conventional edge thickness measuring method; Fig. 9 is a schematic diagram showing a relation between the measured edge thickness and the edge shape ground by the grinder according to a conventional edge thickness measuring method. DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment of the present invention will be described hereinafter with reference to the accompanying drawings. Fig. 1 is a block diagram showing a constitution of the embodiment of the edge thickness measuring apparatus according to the present invention. In this embodiment, employed are the identical characters to the same of similar components as the components in the conventional edge thickness measuring apparatus (mentioned above) disclosed in Japanese Patent Application No. SHO 60-115079, in order to avoid duplication of the explanation. A first arithmetic circuit 32 in Fig. 1 calculates an edge thickness information (Δ i , ϑ i ) from a front and back surface position informations ( f Z i , ϑ i ), ( b Z i , ϑ i ) of a material lens L as a lens to grind which is detected by detectors 24A,24B. This first arithmetic circuit 32 also connects with a comparison circuit 41. The comparison circuit 41 connects with a grinder shape memory 42 which keeps memorizing an already-known V-edge base width W and a V-edge height H. The second arithmetic circuit 43 connects with a lens rim shape memory 18 of a frame shape measuring apparatus 10, the comparison circuit 41, and the grinder shape memory 42. The lens rim shape memory 18 memorizes the all round radius vector information (hereinafter referred to as radius vector information, for brevity) (ρ i , ϑ i ) (with i = 0,1,2,3,...N) can be identical with a value measured by the frame shape measuring apparatus 10 such as the conventional apparatus disclosed in Japanese Patent Publication No. SHO 60-115079, or with data memorized in a memory means such as a floppy disk or an IC card, or with data from a framemaker or the agent by the on-line information processing system. The length ρ i of the radius vector of the radius vector information (ρ i , ϑ i ) (with i=0,1,2,3,...N) of the lens rim from the lens rim shape memory 18 is input in a second arithmetic circuit 43, which subtracts the V-edge height H memorized in the grinder shape memory 42 from the length ρ i and obtains, as shown in Fig. 2, the length ρ i ′ of the measuring radius vector of the all round measuring radius vector information (hereinafter referred to as measuring radius vector information) (ρ i ′, ϑ i ) by the following formula: ρ i ′ = ρ i -H The memory 18 and the second arithmetic circuit 43 act as an input means and an arithmetic means, respectively. The length (ρ i ′) obtained is input in a pulse motor 29. The pulse motors 25,29 are driven and controlled by the second arithmetic circuit 43, corresponding to the measuring radius vector information (ρ i ′, ϑ i ). The driving of the pulse motors 25,29 makes the lens feelers 23A,23B move to position them (23A,23B) at the measuring point ρ i (as shown in Figs. 3A,3B). The feelers 23A,23B positioned there abut on the lens L by elasticity of the springs 25A,25B. The moving amount of the lens feelers 23A,23B is detected in terms of the front and back surface position informations ( f Z i , ϑ i ), ( b Z i , ϑ i ) of the lens L by the detectors 24A,24B. And then, as shown in Figs. 3A,3B, the first arithmetic circuit 32 calculates the Δ i of the edge thickness information (Δ i , ϑ i ) of the lens L at the measuring point i on the basis of the information ( f Z i , ϑ i ), ( b Z i , ϑ i ) as follows: Δ i = b Z i - f Z i The measurement of the edge thickness is carried out over the all round of the radius vector locus S to be measured, that is, all of the measuring points from the 0-th measuring point to the N-th measuring point. The first arithmetic circuit 32 acts as an edge thickness measuring means. The edge thickness information (Δ i , ϑ i ) (with i=0,1,2,3,...N) calculated by the first arithmetic circuit 32 is compared with the width (W) of the V-edge base of the V-edge grinder G memorized in the grinder shape memory 42 by the comparison circuit 41. And selected is a measuring radius vector having an edge thickness narrower than the width W. The grinder shape memory 42 acts as a memorizing means and the comparison circuit 41 acts as a comparing means. Fig. 3A shows the lens L as a minus lens. In this case, selected are a partial measuring radius vector information (Δ j ′, ϑ j ) (with j=a,a+1,a+2,...b-1,b) which defines the partial measuring locus S₁ of measuring points P a and P b , and a partial measuring radius vector information (ρ j ′, ϑ j ) (with j=c,c+1,c+2,...d-1,d) which defines the partial measuring locus S₂ of a measuring points P c and P d . Fig. 3B shows the lens L as a plus lens. In this case, selected are a partial measuring radius vector information (ρ j ′, ϑ j ) (with j=c,c+1,c+2,...d-1,d) which defines a partial measuring locus S₂ of measuring points P c and P d , and a partial measuring radius vector information (ρ j ′, ϑ j ) (with j=g,g+1,g+2,...h-1,h) which defines a partial measuring locus S₄ of measuring points P g and P h . And these measuring radius vector lengths ρ j ′ and edge thicknesses Δ j are input into the second arithmetic circuit 43. Referring to Fig. 2, if the edge thickness Δ j is approximately equal to the edge thicknesses Δ j ′, the proportion of H to W is: H:W = (H-d j ):Δ j where H is a V-edge height and W is a V-edge base width of a V-edge grinder G and d j is a compensated amount. And therefore, the amount d j is: The second arithmetic circuit 43 obtains the length ρ j ″ of a re-measuring radius vector of the partial re-measuring radius vector information (ρ j ″, ϑ j ) by employing the length ρ j ′ and the above amount d j as follows: ρ j ″ = ρ j ′+d j And then the second circuit 43 inputs the re-measuring radius vector length ρ j ″ to the pulse motor 25 and the re-measuring radius vector angle ϑ j to the pulse motor 29. The pulse motors 25,29 driven and controlled based on these inputs move the lens feelers 23A and 23B to the positions 23A′, 23B′ as shown in Fig. 2. By this movement, the lens feelers 23A and 23B measure the front and back surface position informations ( f Z j ′, ϑ j ), ( b Z j ′, ϑ j ) of the lens L on the partial re-measuring loci S₁′ through S₄′ as shown in Figs. 3A and 3B. After the measurement of the informations, the calculation of the V-edge apex position, the display of the image, the determination of the radius vector for grinding, and the grinding are each carried out in the circuit (not shown), as disclosed in the above mentioned Japanese Patent Application No. SHO 60-115079. Figs. 4 and 5 are schematic illustration showing another edge thickness measuring method with the above mentioned edge thickness measuring apparatus. First, all kinds of the length of the radius vector of the radius vector information (ρ i , ϑ i ) (with i=0,1,2,...N) from the lens rim shape memory 18 are input to the second arithmetic circuit 43. The second circuit 43 obtains the measuring radius vector information (ρ i ′, ϑ i ) (with i=0,1,2,...N) by the formula (1), that is, by subtracting the V-edge height memorized in the grinder shape memory from all (ρ i ) s. Second, the second arithmetic circuit 43 inputs the 0-th measuring radius vector (ρ₀′) in the pulse motor 25 and the 0-th radius vector angle (ϑ₀). The driving of the pulse motors 25,29 makes the lens feelers 23A,23B move to the measuring point P₀ (see Figs. 3A and 3B). The lens feelers 23A,23B at the point P abut on the lens L by elasticity of the springs 25A,25B. The moving amount of the lens feelers 23A,23B are detected as the 0-th front surface position information ( f Z₀, ϑ₀) and the 0-th back surface position information ( b Z₀, ϑ₀) of the lens L by the detectors 24A,24B. The first arithmetic circuit 32 calculates the Δ₀ of the 0-th edge thickness information (Δ₀, ϑ₀) at the 0-th measuring point P₀ from the informations ( f Z₀, ϑ₀), ( b Z₀, ϑ₀). The calculation is performed by the following formula similar to the (2) : Δ₀ = b Z₀- f Z₀ And then, the 0-th edge thickness information (Δ₀, ϑ₀) calculated by the first circuit 32 is compared with the V-edge base width W of the V-edge grinder G memorized in the grinder shape memory 42. The 0-th edge thickness Δ₀ is broader than the V-edge base width W in the example of Fig. 4. Therefore, the second arithmetic circuit 43 inputs the length ρ₁′ of the 1st measuring radius, vectorwhich follows the 0-th thickness into the pulse motor 25 and the first radius vector angle ϑ₁, into the pulse motor 29. And the lens feelers 23A,23B are moved to and placed at the first measuring position P₁. The moving amounts of the lens feelers 23A,23B are detected in terms of the first front surface position information ( f Z₁, ϑ₁) and the first back surface position information ( b Z₁, ϑ₁) of the lens L by the detectors 24A,24B. And the first arithmetic circuit 32 calculates the Δ₁ of the first edge thickness information (Δ₁, ϑ₁) at the first measuring point P₁ from the information ( f Z₁, ϑ₁), ( b Z₁, ϑ₁) the same as (2′). Next, the first edge thickness information (Δ₁, ϑ₁) calculated by the first arithmetic circuit 32 is compared with the V-edge base width W of the V-edge grinder G memorized in the grinder shape memory 42 by the comparison circuit 41. The first edge thickness Δ₁ is broader than the V-edge base width W in the example of Fig. 4. The same procedures are in order followed to the j-th measuring radius vector information (ρ j ′, ϑ j ) judged that the edge thickness Δ j is narrower than the V-edge base width W. If the comparison circuit 41 judges that the j-th edge thickness Δ j in the j-th measuring radius vector information (ρ j ′, ϑ j ) is narrower than the V-edge base width W as shown in Fig. 5(a), the second arithmetic circuit 43 changes the length ρ j+1 ′ of the (j+1)th measuring radius vector of the (j+1)th measuring radius vector information (ρ j+1 , ϑ j+1 ) into the first compensated radius vector length τ j+1 as shown in Fig. 4. The first compensated amount t₁ is obtained the same as the formula (4): where W is the width of the V-edge base of the V-edge grinder G and H is the V-edge height. And the first compensated radius vector length τ j+1 is : τ j+1 = ρ j+1 ′+t₁ The second arithmetic circuit 43 inputs the first compensated radius vector length τ j+i into the pulse motor 25 and the first compensated radius vector angle ϑ j+i (equivalent to the (j+i)th measuring radius vector angle ϑ j+i ) into the pulse motor 29. And the lens feelers 23A and 23B are moved to the position of the first compensated measuring point T j+1 in Figs. 4 and 5(b) based on these inputs. And then the first arithmetic circuit 32 obtains the j+1 edge thickness Δ j+1 from the front and back surface position informations of the lens L at the first compensated measuring point T j+1 . The comparison circuit 41 compares the (j+1)th edge thickness Δ j+1 with the j-th edge thickness Δ j preceding to Δ j+1 . If the (j+1)th edge thickness Δ j+1 is narrower than the j-th edge thickness Δ j just before the Δ j+1 as shown in Fig. 5(b), the second arithmetic circuit 43 changes the following (j+2)th measuring radius vector length ρ j+2 ′ of the (j+2)th measuring radius vector information (ρ j+2 ′, ϑ j+2 ) into the second compensated radius vector length τ j+2 as shown in Fig. 4. Therefore, the second compensated amount t₂ is obtained the same as the formula (6). That is : and the second compensated radius vector length τ j+2 is: τ j+2 = ρ j+2 ′+(t₁+t₂) The second arithmetic circuit 43 inputs the second compensated radius vector length τ j+2 into the pulse motor 25 and the second compensated radius vector angle ϑ j+2 (equivalent to the (j+2)th measuring radius vector angle ϑ j+2 ) into the pulse motor29, respectively. The lens feelers 23A,23B move to the second compensated measuring point T j+2 shown in Fig. 4 and Fig. 5(c) based on these inputs. After the measurement of the front and back surface position informations of the lens L at the second compensated measuring point T j+2 , the first arithmetic circuit 32 obtains the (j+2)th edge thickness Δ j+2 . The comparison circuit 41 compares the (j+2)th edge thickness Δ j+2 with the (j+1)th edge thickness preceding to the (j+2)th thickness. If the (j+2)th edge thickness Δ j+2 is narrower than the preceding (j+1)th edge thickness as shown in Fig. 5(c), the second arithmetic circuit 43 changes the following (j+3)th measuring radius vector length ρ j+3 ′ of the (j+3)th measuring radius vector information (ρ j+3 ′, ϑ j+3 ) into the third compensated radius vector length τ j+3 . And the third compensated amount t₃ is obtained the same as in the formula (6). That is : where H is the V-edge height of the V-edge grinder G and the Δ j+2 , Δ j+1 are the edge thicknesses. And the third compensated radius vector length τ h+3 is : τ j+3 = ρ j+3 ′+(t₁+t₂+t₃) The second arithmetic circuit 43 inputs the third compensated radius vector length τ j+3 into the pulse motor 25 and the third compensated radius vector angle ϑ j+3 (equivalent to the (j+3)th measuring radius vector angle ϑ j+3 ) into the pulse motor29, respectively. And then the lens feelers 23A,23B are moved to the third compensated measuring point T j+3 as shown in Figs. 4 and 5(d). And then the lens feelers 23A,23B are moved to the third compensated measuring point T j+3 as shown in Figs. 4 and 5(d). The front and back surface position information s of the lens L as the third compensated measuring point T j+3 are measured, and then the first arithmetic circuit 32 calculates the (j+3)th edge thickness Δ j+3 . And the comparison circuit 41 compares the (j+3)th edge thickness Δ j+3 with the preceding (j+2)th edge thickness Δ j+2 . If the (j+3)th edge thickness Δ j+3 is broader than the preceding (j+2)th edge thickness and narrower than the V-edge base width W of the V-edge grinder as shown in Fig. 5(d), the second arithmetic circuit 43 changes the following (j+4)th measuring radius vector length ρ j+4 ′ of the (j+4) measuring radius vector information (ρ j+4 ', ϑ j+4 ) into the fourth compensated radius vector length τ j+4 as shown in Fig. 4. And the fourth compensated amount t₄ is obtained the same as in the formula (6). That is : where H is the V-edge height of the V-edge grinder G and the Δ j+3 , Δ j+2 are the edge thicknesses. And the fourth compensated radius vector length τ j+4 is : τ j+4 = ρ j+4 ′+(t₁+t₂+t₃+t₄) where t₄ is the negative number. The second arithmetic circuit 43 inputs the fourth compensated radius vector length τ j+4 into the pulse motor 25 and the fourth compensated radius vector angle ϑ j+4 (equivalent to the (j+4)th measuring radius vector angle ϑ j+4 ) into the pulse motor29, respectively. And then the lens feelers 23A,23B are moved to the fourth compensated measuring point T j+4 as shown in Figs. 4 and 5(e). The front and back surface position information s of the lens L as the fourth compensated measuring point T j+4 are measured,and then the first arithmetic circuit 32 calculates the (j+4)th edge thickness Δ j+4 . And the comparison circuit 41 compares the (j+4)th edge thickness Δ j+4 with the preceding (j+3)th edge thickness Δ j+3 . If the (j+4)th edge thickness Δ j+4 is equal to or broader than the V-edge base width W of the V-edge grinder G as shown in Fig. 5(e), the following (j+5)th measuring radius vector information (ρ j+5 ′, ϑ j+5 ) does not need to be changed,and the measuring of the edge thickness at the measuring point T j+5 on the measuring radius vector locus S as shown in Fig. 5(f) is carried out. As mentioned above, in case the measuring edge thickness Δ j first turns narrower than the V-edge base width W, the following first compensated measuring radius vector length τ j+1 for the (j+1)th measuring radius vector ρ j+1 ′ is changed from the first compensated amount t₁ of the formula (6) to the formula (7): τ j+1 = ρ j+1 ′+t₁ And the (j+1)th edge thickness is measured at the (j+1)th measuring point T j+1 as a changed position. Referring to the measurement following to the (j+i)th, the second compensated measuring radius vector length τ j+2 and the measuring edge thickness Δ j+m-1 preceding to the τ j+2 is changed into the (m)th compensated measuring radius vector length τ j+m broader than the V-edge base width W. The (m)th compensated amount tm in a generalized formula of the formulas (8) through (13) is expressed as follows : And the (m)th compensated measuring radius vector length τ j+m is: τ j+m = ρ j+m '+t m (with m=2,3,4,...M. M<N, in both (14) and (15)) In case the measured edge thickness is narrower than the width W of the V-edge base of the V-edge grinder G as mentioned above, the measurement of the thickness is carried out at the compensated measuring point on the compensated locus S′ shown with the stitch line in Fig. 4. And thus,the present invention can provide a method and an apparatus for measuring the edge thickness of a spectacle lens, which has an advantage to measure more accurately the edge thickness of the lens narrower than the width of the V-edge base of the V-edge grinder in comparison with the prior art.

Claims: A method for measuring the edge thickness of a spectacle lens comprising the steps of: inputting an all round radius vector information (ρi, ϑi) of a spectacle frame lens rim for framing said lens (with i=0, 1, 2, 3... N) obtaining an all round measuring radius vector information (ρi', ϑi) by subtracting a V-groove depth (H) of a grinder (G) from the length (ρi) of the radius vector of said all round radius vector information (ρi, ϑi) ; and obtaining an edge thickness information (Δi, ϑi) corresponding to said all round measuring radius vector information (ρi', ϑ i) by measuring a front side refractive position information (fZi, ϑi) and a back side refractive position information (bZi, ϑi) of said lens corresponding to said measuring radius vector information (ρi', ϑi) in order to obtain an edge thickness information (Δi, ϑi) at the grinding position and a V-edge apex position information (kZi, ρi, ϑi) when the edge of said lens is ground with said grinder (G); characterised by: a first step of comparing a width (W) of a grinding base of said grinder (G) with said measured edge thickness (Δi) and selectively obtaining a partial measuring radius vector information (ρj', ϑj) (j ≦ i) of said lens where a narrower edge thickness (Δj) than said width (W) is measured; a second step of obtaining, by presuming that an edge thickness (Δj') in the position of an again measuring radius vector length (ρj'') of a partial and again measuring radius vector information (ρj'', ϑj) (with j≦i) for forming a V-edge of said lens by said V-groove of said grinder (G) in a position corresponding to said partial measuring radius vector information (ρj', ϑj) is approximately equal to said edge thickness (Δj), a measuring radius vector length (ρj'') of said partial measuring radius vector (ρj', ϑj) from said partial measuring radius vector information (ρj'', ϑj) (j ≦ i) as follows: ρj'' = ρj'+dj dj = (1-Δj/W).H (with j ≦ i); and a third step of measuring said front side refractive position informatin (fZi', ϑi) and said back side refractive position information (bZi', ϑi) of said lens in such a manner as to correspond to said partial and again measuring radius vector information (ρj'', ϑj) which are used for obtaining said V-edge apex position information for grinding the edge of that portion of said lens having said edge thickness (Δj) with said grinder (G). A method for measuring the edge thickness of a spectacle lens comprising the steps of: inputting an all round radius vector information (ρi, ϑi) of a spectacle frame lens rim for framing the lens (with i=0, 1, 2, 3...N); obtaining an all round measuring radius vector information (ρi', ϑi) by subtracting a V-groove depth (H) of a grinder (G) from the length (ρi) of the radius vector of said all round radius vector information (ρi, ϑi); and obtaining an edge thickness information (Δi, ϑi) corresponding to said all round measuring radius vector information (ρi', ϑi) by measuring a front side refractive position information (fZi, ϑi) and a back side refractive position information (bZi, ϑi) of said lens corresponding to said measuring radius vector information (ρi', ϑi) in order to obtain an edge thickness information (Δi, ϑi) in the grinding position and a V-edge apex position information (kZi, ρi, ϑi) when the edge of said lens is ground with said grinder (G) ; characterised by: a first step of comparing a width (W) of a grinding base of said grinder (G) with an edge thickness (Δi) of said edge thickness information (Δi, ϑi) to obtain partial measuring radius vector information (ρj', ϑj) (with j ≦ i) in which a measured edge thickness (Δj) is less than said width (W) of the grinding base; a second step of obtaining a compensation value t1 according to the following formula: t1 = (1- Δj W )·H on the supposition that, if said measured edge thickness (Δj) less than said width (W) is obtained from j-th partial measuring radius vector information (ρj', ϑj) of a j-th measurement ("-th" is a suffix representing an ordinate number), an edge thickness of j+1-th partial measuring radius vector information (ρj+1', ϑj+1) is defined as (Δj') and, in addition, the edge thickness (Δj') is approximately equal to said measured edge thickness (Δj); a third step of obtaining a compensating radius vector length (τj+1), which corresponds to a length (ρj+1') of the measuring radius vector of said j+1-th partial measuring radius vector information (ρj+1', ϑj+1), according to the following formula: τj+1 = ρj+1'+t1 and obtaining compensating measuring radius vector information (τ j+1, ϑj+1) about said compensating radius vector length (τj+1) and about a radius vector angle (ϑj+1) of said j+1-th partial measuring radius vector information (ρj+1', ϑj+1); a fourth step of measuring an edge thickness (Δj+1) by measuring front and back side refractive position information of said lens according to said compensating measuring radius vector information (τj+1, ϑj+1); a fifth step of comparing said measured edge thickness (Δ j+1) with said preceding measured edge thickness (Δj), and, if said measured edge thickness (Δj+1) is less than said preceding measured edge thickness (Δj), obtaining a compensation value tm according to the following formula: where Δj+m is an edge thickness of measuring radius vector information (ρj+m', ϑj+m) and Δj+m-1 is an edge thickness of measuring radius vector information (ρj+m-1', ϑj+m-1) precedent to said measuring radius vector information (ρj+m', ϑj+m)(with m=2,3,4,···M,M<N), the edge thickness (Δj+m) being approximately equal to said edge thickness (Δj+m-1); a sixth step of obtaining a compensating radius vector length (τj+m), which corresponds to a length (ρj+m') of the measuring radius vector of said measuring radius vector information (ρj+m', ϑj+m), according to the following formula: τj+m = ρj+m'+tm and obtaining compensating measuring radius vector information (τ j+m, ϑj+m) about said compensating radius vector length (τj+m) and about a radius vector angle (ϑj+m) of said measuring radius vector information (ρj+m', ϑj+m); and a seventh step of successively measuring front and back side refractive position information of said lens according to said compensating measuring radius vector information (τj+m, ϑj+m).

Inventors: WATANABE TAKAHIRO C O KABUSHIK, WATANABE, TAKAHIRO, C/O KABUSHIKI KAISHA TOPCON
Applicants: TOPCON CORP, KABUSHIKI KAISHA TOPCON
Application year: 1990
Main classification: B24B9
IPC codes: G02C7, B24B13, G01B21, B24B9, B24B47