Ruler null for quadratic curve of parabola, hyperbola and ellipse

摘要

PURPOSE:To accurately draw a parabola on drawing paper by the line drawing jig provided to one end of a semicircular arc rail by constituting a ruler of a diamond-shaped link frame provided with four corners in a freely variable manner, two straight rails and the semicircular arc rail. CONSTITUTION:A straight rail 2 is fixed to be set to a Y-axis and a fixing jig 1 is provided at the position of the focus F of a parabola desired to be drawn with respect to the Y-axis. The apex A becoming the fulcrum of a diamond-shaped link frame (a) is fixed to the fixing jig 1 so as to be let coincide with the focus F. A slide 3 is slid along the straight rail 2. Since one apex C of the link frame (a) moves when the slide 3 slides, the link frame (a) moves while revolves around the apex A in a state keeping four sides thereof equal. At this time, the slide 3 slides with the movement of the link frame (a) with respect to the straight rail 2 and a circular arc rail 7 and the position of the other end of the circular arc rail 7 moves. Since the line drawing jig 8 provided to the other end of the circular arc rail 7 is prescribed so as to move along a straight line rail 4, the line drawing jig 8 draws a parabola whose focus is F accurately.