of perpendicular opening and closing shaft 105 is directly transmitted to the front cover engagement portion 203 as shown in fig8 the shape of the cross section of cover 408 is not subject to any special restriction if the shape is such that cover 408 engages with front cover engagement portion 203 and hence the rotation of perpendicular opening and closing shaft 105 is transmitted to upper unit 2 next the operation of perpendicular opening and closing shaft 105 will be explained rotating cam a 404 is fixed to shaft 402 and is rotated together with shaft 402 fixed cam a 403 fixed to cover 408 and rotating cam a 404 are provided so that rotating cam a 404 and fixed cam a 403 are engaged with each other when upper unit 200 is in a closed 0 degree state to produce suction torque of the closed side 0 degree similarly fixed cam b 407 fixed to cover 408 and rotating cam b 406 are provided so that rotating cam b 406 and fixed cam b 407 are engaged with each other when upper unit 200 is in an opened 180 degree state to produce suction torque of the opened side 180 degree next the assembly of.