JPS6295205A - Control of heating and compression of plastic lens - Google Patents

Abstract

PURPOSE:To control the thickness of a fluidized bed to be provided with the shape of the surface of a lens properly and reduced variability in accuracy by a method wherein the compression speed, compression pressure and amount of compression displacement of a forming mold in the heating process of a lens blank is controlled to control the thickness of the fluidized bed. CONSTITUTION:In the heating process of a lens blank, a controller 20 measures the amount of displacement of the parting surface of a mold through a compression displacement sensor 17 and a displacement converter 18 based on a position where the lens blank is abutted against the surface of a cavity and controls the flow amount of operating oil, supplied to a compression cylinder 8, through a power amplifier 21 and an electric hydraulic pressure controller 10 so that the compression speed becomes a set value. The controller 20 switches the speed control of the heating process of the blank into the pressure control of a compression process through a pressure sensor 13 and a pressure converter 14 when a compression pressure has arrived at a switching pressure set in a setter 19. According to this method, the heated fluidized bed of the lens blank can be controlled in the optimum condition to minimize the fluctuation of forming condition in every forming cycle.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a plastic lens molding apparatus, and particularly to a control method suitable for stabilizing heating and compression conditions.

[Background of the invention]

Plastic lenses are lighter than conventional glass lenses and have superior productivity, so they are expected to have a cost-reducing effect.

For this reason, it is widely used in optical products such as projection lenses for projection televisions.

Methods for molding these plastic lenses include a casting method and an injection molding method.

In the casting method, the amount of shrinkage associated with polymerization is large, making it difficult to shape the lens surface with high precision.

On the other hand, injection molding has problems such as deterioration in precision due to molding defects such as sink marks due to temperature distribution accompanying changes in lens thickness, and molding distortion due to thermal stress.

For this reason, a method has been proposed in which plastic lenses, such as projection lenses for projection televisions, are large, thick, and require high precision, and are manufactured using a heat compression molding method. (Japanese Patent Application Laid-Open No. 58-49218) However, the molding conditions such as lens blank shape, blank precision, and mold temperature are likely to vary, and the thickness of the fluidized bed, which has a large effect on lens surface precision, changes accordingly. For this reason, there was a problem in that it was difficult to properly control the fluidized bed to stabilize the lens surface precision and reduce variations. It is an object of the present invention to provide a molding control method for appropriately controlling layer thickness and obtaining plastic lenses with small variations in precision.

[Summary of the invention]

Therefore, in the present invention, in order to prevent molding defects and molding defects caused by fluctuations in molding conditions, the compression speed, compression pressure, and compression displacement amount of the molding die in the heating process of the lens blank are controlled, and the fluidized bed is The feature is that the thickness can be controlled.

[Embodiments of the invention]

The following describes the heat compression molding of plastic lenses according to the present invention. FIG. 1, which explains the control based on the drawings, is a block diagram showing an example of a plastic lens heat compression molding apparatus and its control apparatus used in carrying out the present invention. In this figure, 1 is blank, 2 is
3 is a molding die, 3 is a cavity formed in the molding die 2, and 4 is a mold temperature control channel used for heating and cooling the lens blank 1. The compression molding machine consists of a fixed platen 5, a movable platen 6, a compression ram 7 and a compression cylinder 8 for driving the movable J-plate 6, and is connected to a hydraulic pressure generation source 9 via an electro-hydraulic control valve 10. There is.

This fashion device is composed of a detection section and a control section according to its function. The detection unit includes a mold temperature sensor 11 and a temperature converter 12 that detect the heating state of the lens blank 1.
, a pressure sensor 16 and a pressure transducer 14 that detect compression pressure applied to the parting surface of the molding die 2, a speed sensor 15 and a speed converter 16 that detect the moving speed of the parting surface, and the parting surface. It consists of a displacement sensor 17 that detects the amount of movement, and a displacement converter 1.

The control unit outputs a control signal to the molding machine based on the input information detected by the setting device 19 and the sensor for setting the heating conditions of the lens blank 1.

Operation of the control 1 device configured in this manner is comprised of a controller 20 that amplifies the control signal, a power amplifier 21 that amplifies the control signal, and an electro-hydraulic control valve 10 that converts the IIIJ# signal into a state quantity of hydraulic oil. will be explained based on the fluctuation behavior of the heating state shown in FIG.

FIG. 2 shows the mold temperature, compression pressure applied to the mold parting surface, moving speed of the mold parting surface, and mold parting surface during the lens molding process according to the present invention using the apparatus shown in FIG. Transfer! This is a metaphor for capturing t171k as a change over time. That is, the changes in the state quantities shown in FIG. 2 are the results of monitoring the process of heating and compressing the lens blank made of acrylic resin shown in FIG. 3 to form the lens shape shown in the fourth quotient.

The molding die 2 is heated by the setting device 19 in the die heating process 22.
The heat medium (
(not shown), the compression mold temperature was 180 cOt.
The temperature is raised by At the 9th point in time when the temperature of the molding die 2 is raised to 180 aO, the lens blank 1 is put into the cavity 3, and a fluidized bed is formed in the lens blank heating step 23. After that, it is pressed and molded in a compression step 24,
In the cooling step 25, the lens surface is cooled to a mold release temperature ao'o and shaped.

The blank heating process 230 control operation of the control device of the present invention will be further explained with reference to FIG.

FIG. 5 shows an enlarged view of the change in the state quantity in the blank heating step 22 among the variation behavior of the state quantity in the entire molding process.

The heating process 23 is started by charging the mold specialty 3 Helen's blank whose temperature has been raised to 180°C. The controller 20 controls the state of the heated fluidized bed formed in the lens blank based on the heating conditions of the setting device 19.

That is, the controller 20 uses the position where the lens blank comes into contact with the cavity surface as a reference, and controls the compression displacement sensor 1.
7. Measure the amount of movement of the mold parting surface via the displacement converter 18, and check that the compression displacement is L! 2, the flow rate of hydraulic oil supplied to the compression cylinder 8 via the power amplifier 21 and the electro-hydraulic control 10 is controlled so that the compression speed of the first section 25 reaches the set value Vl.

Similarly, the second section 2 whose compression displacement is between L12 and L23
Control the compression speed of the third section 27 so that the compression displacement exceeds L23.
control so that When the compression displacement increases and the blank 1 comes into contact with the entire surface of the mold cavity 3, a uniform fluidized layer is formed over the entire surface of the lens blank, and the compression pressure increases rapidly. The controller 20 includes a pressure sensor 13,
The pressure transducer 14 is used to constantly monitor this compression pressure, and when the compression pressure reaches the switching pressure P set by the setting device 19, from the speed control of the blank heating pressure 823,
The control mode is switched to pressure control in the compression process 24.

As explained above, according to the present invention, the optimal speed of fluidized bed formation in the blank heating process is set according to the lens shape,
It becomes possible to control.

Furthermore, the compression speed that depends on the fluidized bed formation is measured by the speed sensor 1.
3. It is constantly monitored via the speed converter 16. If a deviation from the set value occurs, a correction signal corresponding to the deviation is output to the power amplifier 21 and the electro-hydraulic servo valve. , it becomes possible to reduce variations in the formation speed of the fluidized bed. If a problem still occurs in the mold temperature control, the mold temperature distribution will be large and the compression pressure required to form a fluidized bed will change. Therefore, the compression pressure will reach the switching pressure PTR of the setting device 19. By setting an allowable blood circumference for the compression displacement LTR at the time when the mold temperature control occurs, it is possible to grasp the trouble in the mold temperature control and reject defective products in which the fluidized bed is incompletely formed. In this case, the compression pressure was detected by a pressure sensor 14 installed on the ink surface of the mold. However, due to constraints such as the Kinken structure.

However, if the pressure sensor 14 cannot be installed in the mold, a pressure sensor can be installed in the compression cylinder 8 to monitor the pressure of the hydraulic fluid supplied to the compression cylinder 8). A similar effect can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to optimally manage the heated fluidized bed of a lens blank, which has an important influence on optical properties, and to produce plastic lenses with excellent optical properties. Molding becomes possible. Furthermore, since the molding state is tracked and controlled, fluctuations in the molding state for each molding cycle can be suppressed to a minimum. As a result, a practical effect was produced in that the conventional molding defect rate could be reduced by 30%.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a control device according to an embodiment of the present invention;
FIG. 2 is a graph showing temporal changes in the molding state according to the present invention, FIG. 3 is a blank shape diagram of a plastic lens according to an embodiment of the present invention, and FIG. 4 is a diagram showing the shape of a plastic lens according to an embodiment of the present invention. FIG. 5, which is a diagram of the shape of a plastic lens, is a graph showing temporal changes in the molding state in the heating compression process in the present invention. 1... Lens blank 2... Molded metal 3... Cavity 13... Pressure sensor 15... Speed sensor 17... ...Displacement sensor 20...Controller 19...Setter 10...Electro-hydraulic control valve 1st 3rd place

Claims (1)

[Claims] 1. In a method of molding a plastic lens by heating and compressing a lens blank with a larger wall thickness and a smaller outer diameter than the finished lens in the cavity of a molding die, the compression displacement, compression pressure, and compression during the heating process of the lens blank A plastic lens characterized by controlling the pressure and flow rate of hydraulic oil supplied to a compression cylinder so that the speed can be measured and the magnitude of compression speed can be programmatically controlled according to a preset compression displacement. Heat compression control method.