Method for the Determination of Residual Moisture on and/or Within a Lens Forming Surface

Abstract

A method for determining residual moisture on and/or within a lens forming surface of a mold half includes the steps of carrying out an infrared inspection of at least a central portion of the lens forming surface of the mold half with the aid of an infrared camera, collecting measurement values resulting from the infrared inspection, which represent a degree of residual moisture on and/or within the lens forming surface, comparing the collected measurement values with a predefined threshold value representing a maximum tolerable residual moisture on and/or within a lens forming surface of a reference mold half, and, upon detection of an exceedance of the predefined threshold value representing the maximum tolerable residual moisture, preventing the inspected mold half from being used further.

Claims

1. A method for determining residual moisture on and/or within a lens forming surface of a mold half, the method comprising the steps of carrying out an infrared inspection of at least a central portion of the lens forming surface of the mold half with the aid of an infrared camera, collecting measurement values resulting from the infrared inspection, which represent a degree of residual moisture on and/or within the lens forming surface, comparing the collected measurement values with a predefined threshold value representing a maximum tolerable residual moisture on and/or within a lens forming surface of a reference mold half, and upon detection of an exceedance of the predefined threshold value representing the maximum tolerable residual moisture, preventing the inspected mold half from being used further.

2. The method of claim 1, wherein upon preventing the inspected mold half from being used further, the inspected mold half is returned to a processing station preceding the infrared inspection for further reduction of the residual moisture, and wherein optionally process parameters within the processing station for reduction of the residual moisture on and/or within the lens forming surface of the mold half are modified.

3. The method of claim 2, wherein the process parameters include temperature, exposure time, flow rate of a venting medium and degree of evacuation.

4. The method of claim 1, wherein by the infrared inspection of the lens forming surface a latent heat of evaporation of liquid over time is determined.

5. The method of claim 3, wherein by the infrared inspection of the lens forming surface a latent heat of evaporation of liquid over time is determined.

6. The method of claim 1, wherein the predefined threshold value representing the maximum tolerable residual moisture on and/or within the lens forming surface of the reference mold half is obtained from infrared inspections of lens forming surfaces of mold halves which have been found acceptable for further processing.

7. The method of claim 6, wherein the predefined threshold value representing the maximum tolerable residual moisture is obtained from an evaluation of latent heat of evaporation of liquid over time measurements of inspected acceptable mold halves of the same kind, i.e. male or female mold halves.

8. The method of claim 7, wherein the predefined threshold (limit) value representing the maximum tolerable (a limit) residual moisture is defined as the minimum change of latent heat of evaporation over time.

9. The method of claim 1, wherein a high resolution infrared camera is used for the infrared inspection of the lens forming surface.

10. The method of claim 9, wherein the high resolution infrared camera used for the inspection of the lens forming surface has a thermal sensitivity better than 50 mK at 30° C.

11. The method of claim 1, wherein in addition to the central portion the lens forming surface is inspected in at least one further portion located radially outwardly from the central portion of the lens forming surface.

12. The method of claim 3, wherein in addition to the central portion the lens forming surface is inspected in at least one further portion located radially outwardly from the central portion of the lens forming surface.

13. The method of claim 1, wherein the lens forming surface inspected with the aid of the infrared camera is the lens forming surface of a male mold half.

14. The method of claim 3, wherein the lens forming surface inspected with the aid of the infrared camera is the lens forming surface of a male mold half.

15. The method of claim 8, wherein the lens forming surface inspected with the aid of the infrared camera is the lens forming surface of a male mold half.

16. The method of claim 1, wherein the inspection of the lens forming surface is carried out after drying the lens forming surface and before electrostatically charging the lens forming surface.

17. An automated manufacturing line for the manufacture of ophthalmic lenses, for example contact lenses such as soft contact lenses, comprising a number of lens manufacturing stations and including cooperating male and female mold halves, which may be assembled to form reusable molds for the manufacture of the ophthalmic lenses from a lens forming material, and comprising a cleaning, rinsing and drying station for the mold halves, and an infrared inspection station for carrying out an inspection of at least a central portion of the lens forming surface of a mold half with the aid of an infrared camera for at least qualitatively determining a degree of residual moisture on and/or within a lens forming surface of the mold half.

18. The manufacturing line of claim 17, wherein the infrared inspection station is arranged ahead of a charging station for electrostatically charging the lens forming surface of at least one of the cooperating male and female mold halves.

19. The manufacturing line of claim 17, wherein the infrared inspection station includes a high resolution infrared camera having a thermal sensitivity better than 50 mK at 30° C.

20. The manufacturing line of claim 18, wherein the infrared inspection station includes a high resolution infrared camera having a thermal sensitivity better than 50 mK at 30° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Further details and advantages of the invention will become apparent from the following description of an exemplary embodiment thereof, reference being made to the drawings which are not to scale, in which:

[0041] FIG. 1 is a schematic representation of a measurement setup for carrying out the method according to the invention; and

[0042] FIG. 2 shows an exemplary graph of measured latent heat evaporation over time which may be obtained by carrying out an infrared inspection of a lens forming surface of a mold half in accordance with the invention.

DESCRIPTION OF EMBODIMENTS

[0043] The measurement setup, which is depicted schematically in FIG. 1, may for example be part of an infrared inspection station which may be included in addition to the various lens manufacturing stations of an automated manufacturing line for the manufacture of ophthalmic lenses, for example contact lenses such as soft contact lenses. The infrared inspection station may for example be arranged in between a cleaning, rinsing and drying station for mold halves and a charging station for electrostatically charging a lens forming surface of at least one of a pair of corresponding male and female mold halves. The measurement setup comprises an infrared camera 1 which is connected with an evaluation unit 2 including an electronic storage unit. The evaluation unit 2 may be equipped with human interface devices for the entry and output of programs and data. Thus, for example the infrared camera 1 may be controlled with the aid of the evaluation unit 2. The evaluation unit 2 may for example be a desktop or a laptop computer. The infrared camera 1 may be a high resolution infrared camera having a thermal sensitivity at or better than 50 mK (milli-Kelvin) at 30° C. Examples for such infrared cameras are the ImageIR® infrared cameras such as the ImageIR® Series 7300 cameras, for example the type ImageIR® 7325, by the company InfraTec GmbH, Dresden, Germany.

[0044] With the aid of the infrared camera 1 a lens forming surface 31 of a mold half 3 may be inspected. The inspection may be concentrated to at least a central portion of the lens forming surface 31. If deemed necessary, in addition to the central portion of the lens forming surface 31 further portions of the lens forming surface 31 may be inspected which are located radially outwardly from the central portion, that is to say in a peripheral portion of the lens forming surface.

[0045] By this infrared inspection the mold half 3 coming from the drying process within the cleaning, rinsing and drying station may be examined for its degree of residual moisture on and/or within the lens forming surface 31. By inspecting the lens forming surface 31 with the aid of the infrared camera 1 a latent heat of evaporation of liquid from the lens forming surface 31 over time may be determined. An example of such measurement values is depicted in FIG. 2. From the obtained measurement values a minimum of latent heat of evaporation ΔT.sub.min in mK/s (milli-Kelvin per second) may be determined, which represents the detected residual moisture of the inspected lens forming surface 31. The so determined value ΔT.sub.min is then compared with a predefined threshold value representing a maximum tolerable residual moisture on and/or within a lens forming surface of a reference mold half, which has been found acceptable for the mold half for being used further, for example for being moved on to the charging station where an electrostatic charge is deposited on the mold half. The predefined threshold value representing the maximum tolerable residual moisture is defined as the minimum change of latent heat of evaporation ΔT.sub.R over time in mK/s of an acceptable reference mold half.

[0046] The predefined threshold value ΔT.sub.R representing the maximum tolerable residual moisture may be obtained from an evaluation of latent heat of evaporation of liquid over time measurements of inspected acceptable mold halves of the same kind, i.e. male or female mold halves. Measurements of latent heat of evaporation over time lead to material specific and water treatment specific graphs which are reproducible and may provide an accurate qualitative representation of residual moisture present on and/or within the lens forming surfaces of the mold halves. The measurements are sensitive with regard to the degree of residual moisture. Ambient influences can be avoided without unreasonable difficulties.

[0047] Upon detection of an exceedance of the predefined threshold value representing the maximum tolerable residual moisture, the inspected mold half is prevented from being used further. Instead, the mold half may be returned to the cleaning, rinsing and drying station preceding the infrared inspection for further drying and reduction of the residual moisture. Optionally, process drying parameters may be modified in order to ascertain a sufficient drying of the lens forming surfaces. The process parameters for optional modification may include temperature, exposure time, flow rate of a venting medium and even a degree of evacuation in case of a drying process involving the application of a vacuum.

[0048] The method according to the invention has been explained by way of example with the aid of an infrared inspection of the lens forming surface 31 of a male mold half 3. It must be noted though, that the infrared inspection may be carried out on both, the lens forming surfaces of male and female mold halves. However, inspection of the lens forming surfaces of the male mold halves only may be sufficient, as air entrapment at the lens forming surfaces of the female mold halves is less likely to happen. Therefore, in embodiments of the lens manufacturing processes it is sometimes abstained from depositing an electrostatic charge on the lens forming surfaces of female mold halves and thus, the problem of residual moisture on the lens forming surfaces of female mold halves is less critical.

[0049] Although the invention has been described with reference to a specific embodiment, it is evident to the person skilled in the art that this embodiment stands only by way of example for the general inventive concept, and that various changes and modifications are conceivable without departing from the teaching underlying the invention. Therefore, the invention is not intended to be limited by the embodiment described, but rather is defined by the appended claims.