The table consists of a large, black granite top, with working surface measuring 2000 mm by 800 mm, flat within .1 mm, and containing a grid of M6 holes for mounting required items. The granite is 254 mm thick and weighs 1200 kg, thus providing a highly stable platform for sample stages, detector, 205 kg detector translation system, and the fast sample exchange system. Total loading on the table will be up to 1500 kg. It must remain stable within 1μm for up to 3 hours. Removeable jacking casters are provided for transporting the system from receiving areas to test and acceptance areas and then to the final destination. Within the hutch, the table will be periodically moved off line when other kinds of experiments are scheduled.
For this purpose, air bearing supports are provided under the frame for ease of movement on the smooth marble floor. In order to avoid the need to survey the table back in parallel to the beam when it is returned to operation, motorized yaw adjustment of +/- 3 degrees is provided. The yaw motion is centered on the nominal sample position. Transverse location of the sample is accomplished within the stack of sample stages. Additional requirements for table movements to accommodate various experiments include motorized vertical movement of 200 mm with a resolution of 0.01 mm, and 2 degrees of pitch movement with a resolution of 0.005 degrees. The center of pitch rotation is directly below the sample. Under the sample is a single jack with capacity of 25 kN and interfacing the table with a spherical plain bearing. At the downstream end there are two jacks with capacity of 10 kN each and tied together with a common drive motor. The interface to the table consists of a line of ball transfer units, ensuring that the table is level transverse the beam.
Tomography experiments require the sample to be rotated in the beam while data is taken. It is important for the sample to be located on the center line of the rotation so each sample must be adjusted within its holder. This is a time consuming function so it is not done during beam time. ADC provides sample holders with a spherical locating feature that features light friction during adjustment and then is securely clamped. A sample tray with an array of up to 49 samples may be preset for measurements. During beam time, the ADC fast sample exchange system moves individual samples from the sample tray to the measurement location which is on top of a stack of translation, tilt, and rotation stages, and then back again. The exchange system can load samples in a predetermined sequence and it is triggered by the measuring system, while also providing TTL signals to indicate completion of its tasks. The gripper is activated by a pulse to an electromagnet and remains gripped until another pulse releases it. Vertical motion is accomplished by a standard ADC slide, which is driven by a stepper motor and can accommodate samples of various heights. Transverse motion is approximately 500mm by stepper motor. The sample tray is mounted to a standard ADC slide to present various rows of samples of the sample tray to the gripper. Total cycle time to exchange a sample is in the order of 7 seconds.