Injection moulding of micro patterned polymer discs for optical rotary encoders

At HSG-IMAT a new concept for optical rotary encoders has been developed. A micro patterned injection moulded polymer disc with a high precision solid measure is the key element of the sensor concept. The micro pattern operates as a diffractive optical phase grating and has lateral dimensions down to 500 nm and a height of about 120 nm. A modified manufacturing process for compact discs and digital versatile discs is used for the fabrication of this polymer encoder disc. The injection moulding of the encoder disc is done by a special modular injection moulding tool which can be adapted to different disc diameters. A basic element in the moulding process is a stamper plate made from nickel, wearing the inverse micro pattern layout. The stamper is manufactured by using an adapted CD/DVD mastering process. With this process a very precise replication of the micro pattern was achieved. Using this manufacturing process, it is possible to fabricate a high precision solid measure for a rotary encoder in high quantities and at low manufacturing costs.