18.104.22.168 Design features of a Z-axis precision manipulator
The use of recirculating ball systems with spindle drive and guidance have several significant advantages over conventional trapezoidal and metric screws drives or sliding guides. Due to their low friction, recirculating ball systems have a high efficiency and it is particularly favorable with large nominal diameters. Despite high external loads (such as the difference in pressure in an evacuated state), they allow for comfortable travel adjustment with a moderate operating force. The previously described stick-slip effect is not present, so that a very fine resolution is available and no breakaway torque will occur, which could make the operation more difficult and have particularly a negative impact on motor drives. Reduction gear that support motors, are not necessary here. Another advantage is the very low level of wear. In a clean environment that does not lead to contamination of the grease, the original lubrication, made of high-quality long-term high-temperature grease, will practically last indefinitely and no maintenance is required.
A guide body that is resistant to bending has a major effect on the precision. The choice of a stable U-shape made of stainless steel leads to greater stiffness with low material input and the associated weight. Inside the U-shape, the guide rail is screwed into the sturdy rear panel. Compared to free-running shaft guides, which cannot be supported, profile rails have a low-deformation structure that implements, even under heavy loads, a precise adjustment in compliance with all spatial axes, across the full travel range.
The bellows unit is typically designed for 10,000 cycles at full use of the travel. The exchangeability of the bellows ensures that manipulators with high quality guide and drive bodies can still be used.
Figure 3.28: Z-axis precision manipulator