[001] The present invention relates to a method and system for bulk disassembling lenses from its glass molds, after their casting. Particularly, the present invention discloses a method and apparatus for bulk demolding of thermally cured plastic ophthalmic lenses from its bulk glass-mold assemblies.

BACKGROUND OF THE INVENTION

[002] Casting is a most economical and popular technology to manufacture bulk ophthalmic stock lenses. During casting process, both male mold and female mold are taped together with appropriate air gap to form the glass mold cavity. The said cavity is filled with polymerizable resin. After polymerization process, the bulk ophthalmic lens is held tightly together with mold surfaces. Demolding is the process of separating the bulk ophthalmic lens from the pair of bulk glass molds.

[003] Currently, demolding of bulk ophthalmic lenses are done manually by applying undue force at the circumferential surface of either male or female mold or both using mechanical leverage. Since glass molds are brittle so ‘the mold separation force’ increases the likelihood of breakage or damage of either the glass molds and bulk ophthalmic lens or both, and reduces the shelf life of glass molds. In addition, the existing process is time consuming and the probability of having scratches or cracks on working surface of molds/lenses is very high. The above mentioned problems led to consuming more number of molds for production, lower lens yield, and increases the manufacturing cost of the product.

[004] In existing techniques, mechanical leverage is majorly utilized to demold the bulk glass molds and the cured lenses of index 1.56. The lateral force against the outer perimeter of the lens mold assembly leads to damage the glass molds.

[005] For lenses having refractive index of 1.49, a peeling method of plastic lens and glass molds separation is disclosed in Japanese Patent No. JPS55123428. This patent is related to the method, wherein glass mold is peeled off from plastic lens after cast polymerization method. It deals with the peeling method of plastic lens and glass mold, wherein glass mold and plastic lens after cast polymerization, are passed through more than 2 liquid vessels having temperature difference, and during the process of peeling the said plastic lens and glass mold, ultrasound irradiation is carried out in the liquid vessels. The four station automatic demolding system with PLC interface is not disclosed in this patent. This prior art does not specify the power of ultrasound, and shape of ultrasonic wave for aiding demolding process.

[006] Further, U.S. Pat. No. 9,102,110 discloses methods and apparatus for separating plastic mold sections, removing a lens product from the separated plastic mold sections, and transferring the lens product to a processing tray. The process includes contacting assembled plastic mold sections with a warm fluid to break fused portions between the mold sections, and using one or more wedge shaped elements to separate the mold sections. The prior art discloses a method for separation of contact lenses from plastic mold assembly and does not disclose bulk glass molds or their assembly.

[007] Conventionally, an ultrasound machine is utilized for cleaning purpose in-which the tank is filled with a liquid. Object to be cleaned is dipped into the liquid. Vibration pattern of alternating low pressure, and high pressure is created by ultrasound in liquid medium which causes tiny bubbles at low pressure called cavitation. Subsequently at high pressure, bubble collapse in liquid medium releasing energy which attack surface of the object, and pulling or removing debris/ dust from the object. The size of the bubble is associated with the frequency of the ultrasound. For example, the bubble size is higher for 28 KHz frequency, whereas for 40 KHz frequency the bubble size is lower. For cleaning purpose, based on the nature of the object, and the type of dirt, the following parameters are optimized: (1) frequency of ultrasound, (2) ultrasound input wave-pattern, (3) intensity of ultrasound, (4) temperature of liquid medium, (5) chemical for cleaning, and (6) concentration/pH value of chemical. Thus, the ultrasound waves in the art are known to only clean dirt and not at all used for demolding.

[008] Thus, there is a need of an effective, time saving and economical method for demolding the bulk ophthalmic lens, specifically the 1.56 refractive indexed lens material, without damaging the bulk glass molds, thus improving shelf-life of the glass molds, enhancing product quality, improving yield.

OBJECTIVES OF THE INVENTION

[009] The primary objective of the present invention is to provide a machine with PLC interface for automatic demolding process for the bulk ophthalmic lenses from its glass molds.

[0010] Another object of the invention is to provide a method for demolding the bulk ophthalmic lenses from its glass molds by application of temperature variation and ultrasonic radiation to reduce bonding at lens mold interface.

[0011] Another objective of the present invention is to provide a time and cost effective demolding process.

[0012] Yet another objective of present invention is to provide an apparatus to disassemble polymerized bulk ophthalmic lenses from its glass molds with temperature variation and pressure developed by ultrasonic radiation to reduce bonding at lens mold interface.

[0013] Other objects and advantages of the present invention will become apparent from the following description taken in connection with the accompanying drawings, wherein, by way of illustration and example, the aspects of the present invention are disclosed.

SUMMARY OF THE INVENTION

[0014] A method and apparatus for demolding the bulk ophthalmic lens from bulk glass molds assembly is proposed, which aid to release the adhesion bond at the interface of the said mold lens surfaces. The method involves differential thermal expansion, and differential thermal contraction between the lens and bulk glass molds under suitable ultrasonic environment. The apparatus disclosed in the invention comprises a tray/zig, lens assemblies, and lenses. The apparatus is designed to accommodate more number of pieces of lens glass mold assembly, and also to reduce scratches in functional area of both lens and glass mold. The apparatus is suitable for bulk demolding process, and reduces the process time and physical damage in molds.

BRIEF DESCRIPTION OF DRAWINGS
[0015] A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when taken in conjunction with the detailed description thereof and in which:

[0016] Figure 1 illustrates a schematic diagram of the automatic demolding machine as per the present invention;

[0017] Figure 2 illustrates an isometric view of the ultrasound demolding machine;

[0018] Figure 3 illustrates a top view of the ultrasound demolding machine;

[0019] Figure 4 illustrates a front view of the ultrasound demolding machine;

[0020] Figure 5 illustrates a side view of the ultrasound demolding machine;

[0021] Figure 6 illustrates a top view of a processing tray with the lens-glass mold assembles; and

[0022] Figure 7 illustrates an isometric view of the processing tray with the lens-glass mold assembles.

[0023] Corresponding reference characters indicate corresponding parts throughout several views. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principals of the invention. The exemplification set out herein illustrates embodiments of the invention, and such exemplification is not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The following description describes various features and functions of the disclosed system. The illustrative aspects described herein are not meant to be limiting. These and other features, including the advantages of the present invention may be incorporated into certain embodiments of the invention which will become fully apparent from the following description.

[0025] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0026] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0027] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention.

[0028] It is to be understood that the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0029] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
[0030] According to the present invention, a method for bulk demolding of lens from a glass mold assembly comprises the steps of loading the plurality of lens-glass mold assemblies onto a tray; loading the plurality of trays onto a basket; transferring the basket onto a first type of tank for primary processing; transferring the processed basket onto a second type of tank for secondary processing; and transferring the further processed basket onto an unloading station for a user to remove the lenses from the glass molds. In both the first and second types of tanks, the lens-glass mold assembles are subject to hot water treatment and simultaneous ultrasound pulse sweeps. The first type of tank is at a temperature range of 60? to 90?, while the second type of tank is at a temperature range of 25? to 40?. The frequency of ultrasound in both the types of tanks is 40KHz. The lens to be demolded as per the present invention may be both concave and convex ophthalmic lens, preferably of refractive index 1.56.

[0031] Additionally according to the present invention, a system for bulk demolding of lens from a glass mold assembly comprises mainly a plurality of tanks; a plurality of material handing baskets; an automatic system for managing the material handling baskets; a plurality of heaters installed on the tanks; a plurality of transducer boxes installed below the tanks; and a programmable logic circuit to control the entire system. The heaters maintain requisite temperatures of water in the tanks and the transducer boxes supply the requisite ultrasound power inside the tank. The plurality of lens-glass mold assemblies are placed onto trays, and further the plurality of trays are placed onto the material handling baskets for processing in the plurality of tanks. The demolding capacity of the present system ranges from 20,000 to 40,000 lenses per day, while the capacity of lens-glass mold assemblies inside each tray ranges from 60 to 126 units.

[0032] In view of the above, the present invention discloses a method and apparatus for demolding bulk ophthalmic lens from bulk glass molds assembly. Particularly, method as per the present invention is applied pursuant to casting of the plastic bulk ophthalmic lenses, specifically lenses of refractive index 1.56. It is understood by a person skilled in the art that after polymerization, the cured lens has a tendency to adhere between the male-glass-mold-surface and the female-glass mold-surface. The demolding method, according to the present invention, aids to release adhesion-bond at the interface of the said mold-lens-surfaces, thus reducing the grip at the interface between the glass molds and bulk ophthalmic lenses and thus, demolding occurs without any damage or scratches in functional area of both lens and the glass-molds. The demolding method involves differential thermal expansion and differential thermal contraction between the lens and bulk-glass molds under suitable ultrasonic environment.

[0033] After primary curing process, the tape which forms mold cavity is removed from glass mold and thermally cured ophthalmic lens assembly. This tape removed assembly of refractive index 1.56 is placed in the tray/zig. In the first stage, the tray is exposed to prescribed step temperature excitation to produce differential thermal expansion between the glass molds and lens, which assist to reduce the strength of the bonding at the interface of bulk ophthalmic lens, and glass molds. The said method includes two stages and only two processing tanks are utilized to avoid repetitive thermal shock on the said assembly.

[0034] The present invention also relates to a system for carrying out the demolding process. The system comprises a four station fully automatic ultrasound demolding apparatus controlled by a Programmable Logic Circuit (PLC) interface that aims to eliminate usage of wedge tools. As shown in Figure 1, the system comprises of four stations: Station 1, Station 2, Station 3 and Station 4 marked as 1, 2, 3 and 4 respectively. There are two processing tanks, primary processing tank (referred to as Processing Tank 1) and secondary processing tank (referred to as Processing Tank 2). There are material handling baskets in all of the said stations. 7a, 7b, 7c and 7d as per Figure 1 represent the presence of a material handling basket in station 1, station 2, station 3 and station 4 respectively. 12a, 12b, 12c and 12d as per Figure1 represent the lens-mold assembly tray inside the material handling basket in station 1, station 2, station 3 and station 4 respectively. As per an embodiment, the complete system as per present invention is constructed using a metal such as steel. An isometric view of said system or machine is illustrated in Figure 2. As per a specific exemplary embodiment, the machine as per present invention has a demolding-capacity of more than 60,000 pieces per day.

[0035] The system disclosed in the present invention comprises of a tray or a zig, lens assemblies, and lenses. This tray is designed to accommodate more number of pieces of lens glass mold assemblies, and also to reduce scratches on the functional areas of both lenses and the glass molds. As per a specific embodiment, a single tray can accommodate 60 to 126 pieces of lens mold assemblies. The tray also facilitates the impact of ultrasonic effect at the interface of glass molds and plastic lens assembly. Further, the tray or zig is preferably positioned above the dead zone of ultrasonic wave in the processing tanks. The present system aids to disassemble polymerized bulk ophthalmic lenses from its glass molds without using mechanical leverages.

[0036] The two processing tanks (2, 3), having identical dimensions, are shown in Figure 2 and Figure 4. A transducer box with ultrasounds is preferably fixed at the bottom of the primary processing tanks (2, 3). As per a preferred embodiment, the transducer box is preferably made-up of stainless steel 316L material. However, a person skilled in the art would acknowledge that any other similar material may also be used for this purpose.

[0037] In Figure 1, 8a and 8b illustrate the ultrasound inside the transducer box in processing tanks 1 and 2 respectively; 13a and 13b illustrate the transducer box at the bottom of the processing tanks 1 and 2 respectively; 9a and 9b illustrate an ultrasound wave in the processing tanks 1 and 2 respectively.

[0038] As per a preferred embodiment, capacities of both the primary processing tank and the secondary processing tank are identical. Both types of processing tanks have separate liquid filling and draining options. For the demolding purpose, a liquid medium is utilized to conduct ultrasound to the lens-mold assembly. 10a and 10b in Figure 1 illustrate presence of hot water in processing tanks 1 and 2 respectively.

Specific Preferred Embodiment - Operation of the Demolding System

[0039] The clear white plastic lens of 1.56 refractive index is casted using monomers (KOC55W and KOC55), preferably supplied by, but not limited to, KOC China. The injected monomer in mold cavity is brought out from an oven after the curing process. Tape is removed from the lens-mould assembly and placed onto the tray to perform demolding operation. It is to be noted that adhesion between the mold and the lens is higher in the monomer KOC55 than KOC55W. Hence, under identical experimental condition and the given composition of raw material, lens is casted.

[0040] Station 1 is a loading station, where an operator loads the tray of lens-mold assembly onto the material handling basket. The system automatically senses the basket and picks the basket containing tray of lens-mold assembly to be demolded. The handling arm shifts the basket to station 2 and releases the basket in the primary processing tank.

[0041] Station 2 comprises of a primary processing tank having liquid, a heating unit and a transducer box. At station 2, as soon as the samples in the tray are dipped into liquid (preferably hot water), the glass molds and plastic lens in the assembly are subjected to uniform step temperature excitation, which causes a thermal expansion of both the materials. The differential thermal expansion of both, the glass molds and plastic lenses, reduces adhesion at interface of bulk-glass-mold and polymerized lens.

[0042] A typical value of thermal expansion of a glass-mold is 60*10 -7/C to 120* 10-7/C, while thermal expansion of lenses are 1200*10-7 /C to 1500*10-7/C. For design, the thermal expansion of glass mold is considered as 95*10-7/C, while that of the lens material is considered as 1350*10-7/C. Thus, the thermal expansion of lens is around 15 times higher than that of the glass molds.

[0043] Simultaneously, lens glass-mold assembly is also subjected to ultrasound true pulse sweep frequency of 40KHz, with an intensity of 4W/inch2. The speed of the ultrasound wave in glass medium is around 2 times faster than that in the polymer or lens medium. When ultrasound travels in different media, it produces turning or bending effect at the interface of the media. The said effect in principal, aids to de-bond the grip between the glass-mold and the lens at its interface. Corning glasses of quartz type molds are preferably used in the present invention.

[0044] The processing time at station 2 is in the range of 30 seconds to 60 seconds, based on the thickness of the lens or the thickness of the glass-mold and lens assembly. After the processing time, the system arm picks up the basket from the primary processing tank 1 and moves to station 3 i.e. towards the next processing tank or the secondary processing tank 2. At the same time, basket 2 from loading station 1 is picked-up and placed in the tank 1. Basket 2 undergoes the same process in tank 1 as explained.

[0045] Station 3 is the secondary processing tank 2 and further processes the basket transferred from the processing tank 1. The temperature of water in the secondary processing tank 2 is preferably between 25? to 40?. This means that the glass-mold and the lens assembly would be hotter than the water in tank 2. Therefore, the glass-molds and the lens would be in differential thermal contraction process in the presence of an ultrasound environment in water.

[0046] After the contraction process, the grip at the interface is completely reduced and gap is created between the glass-mold and the lens. The said gap allows water to fill in between the glass-mold and the lens. After the said process, the basket with demolded glass-mold and lens assembly is picked by an automatic basket handling system and transferred to station 4 or the unloading station. At the same time, the process basket 2 at tank 1 is placed in tank 2.

[0047] As mentioned, pursuant to processing the basket from tank 1 and tank 2, the automatic basket handling system drops the basket with the tray consisting of demolded glass-mold and lens at the unloading station. An operator will remove the tray and the basket. The basket can be used again in the loading station. The tray with the demolded glass-mold and lens are separated gently by hands without applying any undue or unwarranted mechanical force. The separated glass-molds are washed and prepared for the next casting, while the separated lenses are washed and subjected to post curing process.

[0048] As per preferred embodiments, the machine utilizes a 4W/inch2 power; the frequency of the ultrasound is 40 +/-3 Khz and each tank has a capacity of 75 liters (or 19.80 gallons); the internal dimension of each processing tank is around 500mm x 500mm x 300mm (which is length x Width x Height respectively); the peak ultrasound power is 4800 Watts. At the bottom of both the processing tanks, separate transducer boxes of 1200 Watts are installed. Both processing tanks have separate liquid filling and draining options. For the demolding purpose, water may be used as a medium to conduct ultrasound to the lens-mold assembly. A 5KW heater is installed to establish a maintenance temperature of 50? to 95? in the primary processing tank 1. In the secondary processing tank 2, a 4KW heater is installed to maintain a temperature of 25? to 40?.

[0049] This four station fully automatic ultrasound demolding system is controlled by a Programmable Logic Circuit (PLC) interface. It preferably comprises of a 7 inch color touch screen, which displays position of the automatic material handling system, the ultrasound function and the temperature of each processing tank.

[0050] As per an alternate embodiment, apart from a fully automatic control, the present invention also provides for optional manual operation and semi-automatic operation. The process time and the conveyor movement are adjustable, as shown in Figure 3.

[0051] As per an additional embodiment, ultrasonic waves with appropriate frequency and power are launched along the direction of perimeter of lens and glass mold assembly. Ultrasonic wave induces pressure to release the grip at the interface of the glass mold and lens. The de-bonding force at the interface is created by said pressure and differential impedance of ultrasound between lens medium and the glass medium. The optimal differential impedance may also be produced by altering the angle of incidence of ultrasound at the interface.

[0052] For demolding application, ultrasound waves are not utilized for cleaning the surface of glass-molds and lens assembly. However, the pressure wave developed by the ultrasound creates a de-bonding force at the interface of the glass-mold and lens assembly due to a differential speed of propagation between the glass-molds and plastic lens. A skilled person in the art would understand that the intensity of ultrasound is higher for a demolding machine, typically 4W/ inch2 to 6W/inch2.

[0053] The time for the demolding process of 1.56 refractive indexed lenses depends on adhesion property of lens resin with glass molds, thickness and geometrical size of the lens, and geometry of the mold. As per a preferred embodiment, under controlled experimental condition, the typical processing time for the first tank varies from 30 seconds to 2 minutes.

[0054] The second stage also has same the processing time, but the input step temperature of second tank is reduced to around 25? to 40? which is above the ambient temperature, so that the mold lens assembly undergoes differential contraction under ultrasonic environment. The bonding between the lens and glass mold are released. Thereafter, the lens is separated from the molds gently by hands without applying undue stress at the circumferential surface of molds.

[0055] Figure 3 illustrates a top view of the system and a preferred embodiment of the present invention, as per which 1 denotes the length of the entire system (which may be around 3070 mm), 2 denotes the width of the machine (which may be around 1087 mm), 3 denotes length and width of the processing tanks, 4 denotes length of the loading and un-loading stations, and 5 denotes separation distance between the adjacent stations.

[0056] Figure 4 illustrates a front view of the bulk demolding system as per present invention, wherein 6 denotes the height of the processing station and 7 denotes height of the machine.

[0057] Figure 6 illustrates a top view of the tray containing the plurality of lens-glass mold assemblies, wherein 1 denotes length of said tray and 2 denotes width of the tray. As per a preferred embodiment of the present invention, the length of the tray may be around 457 mm and the width of the tray may be around 442 mm.

[0058] The operating temperature of both the tank should preferably be maintained above ambient temperature to improve shelf life of glass molds. And to ensure the quality of lenses, maximum temperature of process tank should be within resin curing temperature. In the bulk ophthalmic mold lens assembly the speed of ultrasonic wave is different for glass molds, and plastic lens, which aid to release the bonding at the interface without damaging the glass molds.

[0059] The proposed invention aids to demold bulk ophthalmic lenses of both concave power and convex power of stock lenses having a refractive index of, but not limited to, 1.56, without requiring application of an external physical pressure on the molds using a mechanical leverage. The present system is suitable for bulk demolding process, and reduces the process time and physical damage to molds. The said process facilitates the separation of lens from the mold quickly, and without damaging the working surfaces of both lens and the molds. The invention also improves the quality of lenses and shelf life of the molds.

[0060] While the present invention has been described with reference to one or more preferred aspect, which have been set forth in considerable detail for the purpose of making a disclosure of the invention, such aspects are merely exemplary and are not intended to be limiting or representing an exhaustive enumeration of all aspects of the invention. The scope of the invention, therefore, shall be defined solely by the following claims. Further, it will be apparent to those skilled in the art that numerous changes may be made in said details without departing from the principles of the invention.

We claim:

1.A method for bulk demolding of lens from a glass mold assembly, comprising the steps of:
a. loading the plurality of lens-glass mold assemblies onto a tray;
b. loading the plurality of trays onto a basket;
c. transferring the basket onto a first type of tank for primary processing;
d. transferring the processed basket onto a second type of tank for secondary processing; and
e. transferring the further processed basket onto an unloading station for a user to remove the lenses from the glass molds,
wherein, in both the first and second types of tanks, the lens-glass mold assembles are subject to hot water treatment and simultaneous ultrasound pulse sweeps.
2. The method for bulk demolding of lens from a glass mold assembly as claimed in claim 1, wherein water in the first type of tank is at a temperature range of 50? to 95?.

3. The method for bulk demolding of lens from a glass mold assembly as claimed in claim 1, wherein water in the second type of tank is at a temperature range of 25? to 40?.

4. The method for bulk demolding of lens from a glass mold assembly as claimed in claim 1, wherein the power of ultrasound in both the types of tanks is 4 W/inch2.

5. The method as claimed in claim 1, wherein the lens to be demolded may be both concave and convex ophthalmic lens of refractive index 1.56.

6. An apparatus for bulk demolding of lens from a glass mold assembly, comprising:
a. plurality of tanks;
b. plurality of material handing baskets;
c. an automatic system for managing the material handling baskets;
d. plurality of heaters installed on the tanks;
e. plurality of transducer boxes installed below the tanks; and
f. a programmable logic circuit to control the present apparatus,
wherein, the heaters maintain requisite temperatures of water in the tanks and the transducer boxes supply the requisite ultrasound frequency inside the tank.
7. The apparatus for bulk demolding of lens from a glass mold assembly as claimed in claim 6, wherein the plurality of lens-glass mold assemblies are placed onto trays.

8. The apparatus for bulk demolding of lens from a glass mold assembly as claimed in claims 6 and 7, wherein the plurality of trays are placed onto the material handling baskets for processing in the plurality of tanks.

9. The apparatus for bulk demolding of lens from a glass mold assembly as claimed in claim 6, wherein the demolding capacity of present apparatus ranges from 20,000 to 60,000 lenses per day.

10. The apparatus for bulk demolding of lens from a glass mold assembly as claimed in claim 7, wherein the capacity of lens-glass mold assemblies inside each tray ranges from 60 to 126 units.