Harmonic Drive
Crystal Pulling Machine Two-speed Range Actuator
Special actuator
Two-speed range actuator
For the latest generation of 300 mm silicon wafers, special demands are made of the machines used to grow the silicon mono-crystals from which the wafers are ultimately produced. A seed crystal is carefully brought into contact with the surface of the molten silicon, and then carefully withdrawn, the mono-crystal growing as a result.
The smooth running of the actuators used to provide this movement is essential to the quality of the crystal and hence the quality of the wafer. The seed crystal is drawn out of the molten silicon with a speed of a few centimetres per hour. Special two-speed range actuators are used for both the rotational movement of the crucible containing the molten silicon as well as the linear movement of the seed crystal.
During creep-feed operation during crystal growth, the extremely slow speed is achieved by a total reduction ratio of 5000:1. This is provided by an FHA hollow-shaft actuator combined with an HDGM precision gearbox.
The innovative combination of brake and clutch makes it possible to operate the actuator in rapid feed with a ratio of 50:1 during the machine set-up. As can be seen from the diagram, the Circular Spline of the HDGM is not fixed, but rather can rotate within the housing. In rapid-feed mode the Circular Spline and Wave Generator of the HDGM are clamped together and rotate with the output speed of the FHA actuator. In creep-feed mode the Circular Spline is fixed and the Wave Generator is driven by the output of the FHA actuator. In this mode both gear reduction ratios are multiplied together.
