FRAME-OPENING AND CLOSING MECHANISM PROVIDED WITH A TORSION BAR

A frame connection member (18) which is fixedly mounted on one of said upper frame part (2A) or lower frame part (2B) is pivotably hinged to the other frame part (2A or 2B) for rotary motion around a horizontal axis shaft line (P). An inversely tapered concavity (c) is formed in said frame connection member (18) for inserting a twisted shaft portion (b) of said torsion bar (16) from a direction meeting at right angles with the axis shaft line (P) of the twisted shaft portion (b). Said frame connection member (18) is provided with a first engagement member (21) for engaging an energizing reaction froce portion (f) on one end side of said torsion bar(16), said other frame part (2A or 2B) is provided with a second engagement member (23) for engaging an energizing reaction force portion ( l ) on the other end side of said torsion bar (16). Said other frame part (2A or 2B) is provided with a rotation limiting member (22) for regulating the angle of rotation of said frame connection member (18) relative to said other frame part (2A or 2B) within a range larger than the opening angle allowed by an open position regulating means (19). The setting of the torsion bar (16) can be very simply and easily achieved by merely inserting said twisted shaft portion (b) of the torsion bar (16) into the inversely tapered concavity (c) sideways and slightly twisting said twisted shaft portion (b).