High Precision Kappa-Goniometer with Fully Motorised Goniometer Head

The International Kappa Workgroup was established withtin BIOXHIT in 2004 to bring all those scientists together who were aiming to use multi-axis goniometers for smart reorientation of the crystalline samples during data collection. The aims cover all aspects from instrument design, and control software development as well as data collection strategy calculations with on-the-fly data processing feedbacks. Although the Kappa Workgroup was initially started by BIOXHIT members, its size has increased very fast and now contains collaborators from the US and Australia.

MK2 mini-Kappa models have been used at ESRF/MRC-BM14 and on the ESRF MX MAD beamlines (Partners 1B and 2). The Kappa head has been extensively tested in terms of collision prevention. Complete calibration to increase precision has been carried out successfully. The STAC software has been installed and is fully available within the DNA interface. The wizard to ease the configuration of the Mini-Kappa's collision parameters in the MD2 has been developed.

The experience with MK2 mini-Kappa has been used to define the modifications for the MK3 version, Figure 3.4.a. Several points were improved including the stiffness of the anti-collision detection system, the stability of the friction breaks, the resistance of the clutch systems to users manipulations (ruby balls/hard tempered steel discs), and finally the stiffness of the Kappa and Phi axis (ceramic ball bearings). Control procedures have been established to fully characterise the devices, and to track their precision over time. Typical SOC (sphere of confusion) of 5 micrometer is now achieved at any kappa angles. The collision map, Figure 3.4.b, is advantageous to the one from currently available devices. The mini-Kappa MK3 version is becoming commercially available from the company ACCEL GmbH, where Partner 1B would be providing training to help the use of mini-Kappa together with the reorientation software STAC.

Figure 3.4.a. The BIOXHIT miniKappa goniometer

The Kappa goniometer was assembled, commissioned and tested at several BIOXHIT Partner sites, including ESRF, SLS and DIAMOND. New, high precision bearings were developed in collaboration with and manufactured by the company ADR. They provide an eccentricity below 1 μm for Kappa and phi and have the opening which is sufficiently wide to insert a slip ring.

Figure 3.4.b. Collision map of the miniKappa goniometer