The lengths of the links comply with the conditions: B͞C=B͞D=M͞F=A͞B=a/2 ans D͞F=B͞M. Figure BDFM is a parallel-crank linkage. Link 1, turning about fixed axis A, is connected by sliding pairs to sliders 7 and 2. Link 3, turning about fixed axis B, is connected by turning pairs C and D to I slider 2 and link 4. Link 4 is connected by turning pair F to link 5 which turns about fixed axis M. Slider 6 is connected to slider 7 by turning pair G and moves along axis Fn of link 4. When link 1 turns about axis A, point G describes cissoid , of Diocles s with the equation y²=x²/(a-x).
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