second tray 1 a as shown in fig4 c please refer to fig5 and 7 which illustrate an explosive view an operational view and a prospective view of a tray positioning device 6 respectively in accordance with the third preferred embodiment of the present invention said tray positioning device 6 comprises a first driving unit 62 and a positioning unit 64 the first driving unit 62 includes a cylinder 621 and a tray push pull rod 623 being secured to the cylinder 621 the positioning unit 64 has a positioning base 641 a positioning block 642 a first positioning spring 643 and a second positioning spring 644 wherein said positioning block 642 further comprises a extruded edge stopper 645 the extruded edge stopper 645 and the second positioning spring 644 are provided in proper locations on the positioning base 641 the first positioning spring 643 is secured to the tray push pull rod 623 a third sidewall 646 and a fourth sidewall 647 are provided on the right hand side of the second positioning spring 644 where it is turns and it is about to turn straight respectively a first sidewall 648 is provided on the positioning block 642 where it faces a tray 71 a second sidewall 649 is provided on the inner side of the extruded edge stopper 645 the first sidewall 648 and the second sidewall 649 are perpendicular to each other please.