device 400 could change the angle while retrieving data the data reading device 400 adjusts the reading angle through the fourth rotating device 318 and hence the angle of retrieving data is variable in order to get a better signal strength between the data reading device 400 and rfid tags when both are vertical each rotating device 312 314 316 318 has a driving motor and a transmission mechanism the driving motors are a motive force source which drive components coupled with each rotating device through transmission mechanisms an included angle 340 between two telescopic devices is variable through controlled driving motors to drive the joint portion of coupled portion for rotation in an embodiment of the present invention the driving motors could be dc servo motors or ac servo motors and the transmission mechanisms are speed reduction devices in fig4 each telescopic device 321 322 323 has an upper arm 401 and a lower arm 402 the lower arm 402 comprises a screw rod 410 a sliding block 420 a driving motor 430 and a transmission device 440 the driving motor 430 is coupled with the transmission device 440 and rotates the screw rod 410 through the transmission device 440 which enables the sliding block 420 to move along the screw rod 410 the sliding block 420 moves in the direction denoted by the arrow 450 shown in fig4.