The lengths of the links comply with the conditions: P͞A=A͞Q=Q͞C=C͞P=b, E͞Q=Q͞H=H͞B=B͞E and D͞A=D͞C=a. Figures PAQC and EQHB are rhombus linkages; figure APCD is a rhomboid linkage. If point Q traces along any curve ρ_Q=ρ_Q(ϕ), where ρ_Q=B͞Q and ϕ is the polar angle made by line DPBQ and axis Bx, then point D describes a curve with the polar equation ρ_D=ρ_D(ϕ). Quantities ρ_Q and ρ_D are related by the condition ρ²_D=ρ²_Q±k² where k²=a²-b²=const.
$771$LW,Ge$