SWITCHING PHASE OPTIMIZING METHOD OF CHARGE CONTROL SIGNAL

PROBLEM TO BE SOLVED: To automatically set the switching phase of a charge control signal so as to maximize stablity allowance with respect to the fluctuations in the pulverizing phase of particles during printing without generating midway charged ink particles. SOLUTION: A phase curve of a jet current is measured (step S101) to calculate the min. value corresponding phase θmin (step S102) and the max. value Imax is extracted (step S103) and a threshold value (Imax-δ) is set (step S104). Next, phase points θp, θp+1,..., θq,..., θr being Ij >= (Imax-δ) are extracted (step S105) and, if a phase interval θT(=θp-θmin) is not an experience value ΔθS or less (step S106), a value of (θq+θw)+θp}/2-Δ is calculated and the switching phase of a charge control signal is set to the most proximate phase point of this value (step S107).