BLOCKMATIC for precision blocking

Description of the BLOCKMATIC
For turning contact lenses, the button must be fixed in the precision lathe. One method for fixing the button is to block it to the chuck, with a layer of wax. For precision processes, if a high quality lens is to be turned, a number of vital conditions must be met, including control of the thickness of the wax layer, and maintaining the parallelism of the lens curves.

Blockmatic

The BLOCKMATIC is the ultimate solution for the high precision blocking of buttons and counter-blocking of finished base curves.
In this production process, the unit performs a range of functions:
• Automatically blocking the flat button centrically, on the chuck.
• Automatically and precisely centrically counter-blocking the machined button with finished base curve and edge.

The unit can be expanded to include:
• Integrated heating element to keep the chucks at the correct temperature.
• Ultrasonic rinsing bath to remove the wax from the contact lenses.
• System for separating the button from the chuck.

Short cycle time

The time required by the Blockmatic for blocking and counter-blocking is extremely short.

• An air cooling system guarantees the controlled cooling of the wax.
• At the simple push of a button, the automated gluing process will block the button, with extreme accuracy, on the pre-waxed chuck.
• Blocking time is only 10 seconds, whilst counter-blocking is completed in approx. 20 seconds (depending on the wax and material used).

Can handle any button

The flexibility of the unit is considerable. The positioning mechanism on the Blockmatic can be easily adjusted, to take various types of chuck, whilst the button holder can be adjusted to suit every button type. As a result, the Blockmatic offers sufficient flexibility for processing thick, thin, large and small buttons. The flexibility of the unit is further displayed by its ability to handle a range of wax types. This capability requires not only
temperature adjustment; the thickness of the wax layer must also be controllable. A micrometer has been fitted to ensure accurate thickness adjustment, thus preventing the lens floating out of position.

High precision

The blocking process on the Blockmatic is subject to a fully automatic PLC control, guaranteeing a high degree of reproducibility. The machine operation need only be occasionally monitored by measuring the lens thickness to guarantee accuracy. The lens thickness is predetermined according to the thickness of the wax layer and the accuracy of the lathe control system. The wax layer thickness on the Blockmatic is adjusted to an accuracy of less than 2 pm, using the micrometer setting device.

The advantages of reproducibility in relation to lens thickness are:

• Possibility for achieving reproducible lens strengths.
• Increased production efficiency.
• Improved lens-wearing comfort for the customer.

Both the blocking and counter-blocking units have high precision guides, guaranteeing a high degree of centricity of the base curve in relation to the front curve. Lens curve parallelism may deviate by less than 5 pm, resulting in excellent lens quality.

Operation

The button must first be blocked, for turning the base curve and edge. This operation is carried out in the left-hand blocking unit. The button is placed in the holding section and held in position by vacuum. A preheated chuck, already coated with its wax layer, is then placed in the lower holder, and the blocking program is activated by pressing the start button:

The upper holder positions the button on the chuck, and applies a preset pressure, for a predetermined period of time. When this preset time expires, the upper holder releases the button, and automatically returns to its upper position, at which point the blocking process is concluded. Once the base curve and edge have been turned on the machine, counter-blocking must be carried out on the right hand unit. In order to carry out centrically accurate counter-blocking, it is that both upper and lower holder extremely accurately positioned.

Special requirements are imposed both chuck holders and chuck, wit respect to hardness and grinding accuracy. The required wax layer thickness is set, using the built-in micrometer. The chuck holding the turned butt (with finished base curve and edge is subsequently placed in the upper holder, and pneumatically clamped into position. The second chuck can then be pneumatically positioned in the tower holder, and the PLC-con trolled counterblocking process can be carried out:

• The upper holder, with the button, is lowered automatically to the preset height.
• The lower chuck is air cooled, to set the wax.
• After 10 to 15 seconds, the upper chuck is released, to prevent any possible tension in the wax layer, as it sets.
• Following further cooling, the lower chuck is also released.
• One chuck is now fixed to each side of the button.
• Following extraction from the unit, the upper chuck can be separated from the button.

At this stage, the button has been counter-blocked, and is fixed accurately and centrically on the second chuck. In other words, a precision process has been carried out, taking account of the specific characteristics of both button and wax. To produce complete lenses including a controlled edge, in exact compliance with the lens design, tight tolerances must be realized. The Blockmatic, with the automated blocking process, ensures that this can be achieved.

Technical specifications
Dimensions on floor: 57 x 47 cm
Electrical power requirements: 220V, 50 Hz, 1 phase, or 110V, 60 Hz, 1 phase
Power consumption: 0,1 kW
Air pressure: 7 bar
Air consumption: 25 NI/mm 216E 501