1) Characteristics of granite stones

- While the granite stones adopted for the large XY table have the following advantages, including 1. Minimum degradation with age, 2. Small thermal expansion rate, 3. Vibration dumping properties, they also have the weakness in the bending rigidity since the material strength is smaller than that of metal.

- Therefore, we needed to develop a technology of enhancing the rigidity in the structure using granite stones. This volume introduces the high rigidity structure for large tables.

2) High rigidity structure for large equipment design

- Fig.1 shows the structure diagram of the linear guide mechanism adopted for an XY table designed in the general machining dimensions (machining area is equivalent to A4 to A3 size.) Since the pneumatic hydrostatic bearing is adopted, it has the bearing shape as shown in Fig.1.

- If you increase the equipment size without modifying the structure, the load will cause a considerable deformation of the table top between the two bearings. As a result, the following problems will occur:

(1) Error in linear motion
(2) Bending of workpiece caused by deformation of the table top
(3) Vibration caused by the unstable pneumatic bearings resulting from deformation of the table top

- In this case, the deformation volume (deflection) in the center of the drive table increases in proportional to the cube of distance between the two guide rails. (Fig.2)

y=W・L³/48E/I
W:Weight, L:Length of beam, E:Young's modulus, I:Second moment of area

- In this case example, an auxiliary rail is installed between the two sliding guides to minimize deflection caused by the table weight. (Fig.3)

- The auxiliary guide in the middle does not work as a bearing for linear motion. It simply supports and reinforces the moving table from the bottom.

- For large automation devices, notice that the flatness of the base plate or slight inclination will have an effect on the assembly precision.