A method for controlling a welding robot having a servo gun with a movable tip and a fixed tip includes the steps of separately contacting a surface of a part with the movable tip to measure a base test point and an at least two additional test points displaced from the base test point. The CVT is selectively operated in either a torque control strategy and a ratio control strategy, depending upon the operating conditions of the vehicle. Due to the use of SbxSe100-x in the phase-change material layer, a higher-speed, lower-power consumption phase-change memory device than a GST memory device can be manufactured. The edges of the respective primary X-ray beams enter a plurality of X-ray blocking portions of the second grating.