Pohang Accelerator Laboratory (PAL) has been developing a SASE X-ray Free Electron Laser based on 10 GeV linear accelerator. The cavity BPM mover was developed to be used in the intersections of the Undulator Systems. The main specifications include submicron repeatability for a 50 kg cavity BPM adjusting system within compact dimensions and a ±1.5 mm stroke in the vertical and horizontal direction. Compact linear motion guide based on 5-phase stepping motors have been chosen. A closed-loop control system has been developed to achieve this repeatability. For the feedback, one digital probe sensor for each axis was used. Mechanical switches are used to limit movement. In addition, hard-stops are included for emergency. In this report, we describe the design of the stages used for precise movement and results of mechanical measurements including reproducibility will be reported. INTRODUCTION PAL-XFEL will provide X-rays in ranges of 0.1 to 0.06 nm for hard X-ray line and 3.0 nm to 1.0 nm for soft Xray line by using the self-amplified spontaneous emission (SASE) Schematic [1][2]. To generate X-ray FEL radiation, the PAL-XFEL undulator section requires high resolution beam position monitoring systems with < 1 ȝm resolution for single bunch. To achieve high resolution requirement, the PAL-XFEL undulator section will use the cavity BPM. It can achieve sub-micron resolution for single pulse measurements by using the resonant mode of cavity. The cavity BPM system will be installed in between each undulator with other diagnostics tools. The cavity BPM Mover had been fabricated, tested and installed for the PAL XFEL. It will be used in the intersections of the Undulator Systems. The inter-undulator sections, shown in Figure 1, consist of phase shifter, quadrupole magnet with mover, beam loss monitor, two corrector magnets and cavity BPM with mover. The position of such diagnostic devices remains fixed with respect to the central dipoles. The main specifications include submicron repeatability for a 10 kg cavity BPM within compact dimensions and a ±1.5 mm stroke in the vertical and horizontal direction. Compact linear motion guides based on 5-phase stepping motors have been chosen. A closed-loop control system has been developed to achieve this repeatability. For the feedback, one digital probe sensor for each axis was used. Mechanical switches are used to limit movement. In addition, hard-stoppers are included for emergency. Figure 1: Lay-out of Inter-Undulator Section OVERVIEW OF CAVITY BPM MOVER Table 1: Main Specification for Movers Value Details Dimensions 332x140x255.5 mm Long, wide, high Axes 2(H & V) ±1.5 mm stroke Load 10 kg Repeatability < 3 ȝm Control Device Digital probe closed-loop EPICS Ranges ±1.5 mm Limit Switch ±1.6 Hard Stopper Driving System 5 Phase Stepping Motor With brakes Measure System Digital Probe (DP/5/S) < 0.15 ȝm Limit Sensor D4E-1C20N The main specifications for these movers are included in Table 1. The movers are composed of each stepping motor for horizontal and vertical, digital probe, limit switch and harder stopper. Figure 2 shows the exploded view of 3D modeling. A robust and compact mover is required according to specifications therefore concept design includes some important features. The drive mechanism adopts a 5-phase stepping motor with ball screw for Oriental Motor’s. The motor achieves high positioning accuracy in a space-saving design. The compact and lightweight body houses the rotating components as well as the linear motion mechanism of the stepping motor. The load position can be held with electromagnetic brake when the power is cut off. Since the work will not fall in case of power failure or disconnection, it can safely use equipment in which the work moves vertically. Linear motion (LM) guides and high-precision motors have been selected for both axes. LM guide in each row of balls is placed at a contact angle Proceedings of IPAC2016, Busan, Korea WEPMR053 07 Accelerator Technology T33 Subsystems, Technology and Components, Other ISBN 978-3-95450-147-2 2395 C op yr ig ht © 20 16 C C -B Y3. 0 an d by th e re sp ec tiv e au th or s of 45° so that the rated loads applied to the LM block are uniform in the four directions (radial, reverse radial and lateral directions). Two digital probes are used to measure at horizontal and vertical direction movement. Figure 2: Exploded view of 3D modelling for cavity BPM Mover. REPEATABILITY TEST The repeatability is the most important specification of the movers, as submicron level must be reached. The testing set up is displayed at Figure 3. The cavity BPM mover is measured at both axes with external reference gauges [3]. The positioning to a certain LVDT position reaches always exactly the same actual position from external references in a perfect repeatable system. The sets of measured movements are 0.2 mm steps along the vertical axis and the horizontal axis for the whole movement range. Results for direct movements from a given position have been found to have very high repeatability. Figure 3: Test set-up for repeatability. Figure 4: Repetition of cavity BPM Mover. Maximum deviation is ±0.6 ȝm of vertical measurement for number 3 Mover. Design has showed also a high ability to keep position under certain possible conditions. Under such conditions, Repeatability is below ± 1 micron at every set of movements for both axes. Figure 4 shows the repeatability of the number 3 cavity BPM mover. Upper graph is the measuring data for horizontal movement and lower is the vertical movement. The maximum deviation is ±0.3 ȝm for horizontal movement and the vertical movement is ±0.6 ȝm.