2 being the support point of rotation on the other hand the rotation of the upper support frame 6 is transmitted to the lower support frame 24 through the interlocking shaft 18 and the lower support frame 24 too rotates horizontally with the round pillar 22 of the lower support bed 21 being the support point of rotation when the upper and lower support frames 6 and 24 start rotating horizontally in the direction represented by arrow in fig1 the door 19 starts rotating towards the sidewall of the entrance on the side of the upper and lower support beds 2 21 as represented by arrow for the links 14 14 30 30 in the upper and lower support frames 6 24 become gradually straight from their bent state with the rotation of the upper and lower support frames 6 24 respectively and when these links 14 14 30 30 become straight the pins 17 33 of the arm rods 12 28 are pushed out as much respectively when the upper and lower support frames 6 and 24 rotate to the positions which are 45 u00b0 from their original positions the links 14 14 30 30 become straight as shown in.