Method of compensating for image quality by controlling toner reproduction curve

A method of compensating for image quality of an printing machine having a color toner density sensor, which is provided over a photosensitive belt, receiving light reflected from test patches having different toner area coverage and converting the received light into an electrical signal to control a developer bias and a grid voltage, the method comprising:

• (a) comparing a toner reproduction curve (TRC) Φ(k) measured by the color toner density sensor with a reference TRC ΦR to obtain a deviation ΔΦ;
• (b) calculating the variation ΔVB of the developer bias VB(k) from a Jacobian matrix JB of a measured developer bias VB(k) to calculate a new developer bias control parameter VB(k+1) and determining a measured grid voltage VG(k) as a new grid voltage control parameter VG(k+1) if the deviation ΔΦ is not less than tolerant deviation ΔΦT;
• (c) obtaining a backplating vector VBP from a difference between the grid voltage control parameter VG(k+1) and the developer bias control parameter VB(k+1);
• and
• (d) initializing a control parameter “a” as “0”, comparing the backplating vector VBP with a minimum critical value VTmin, performing operation (e) if the backplating vector VBP is smaller than the minimum critical value VTmin, and performing operation (g) if the backplating vector VBP is greater than the minimum critical value VTmin;
• (e) increasing the control parameter “a” by an increment “α”, setting control parameters VG(k+1) and VB(k+1) based on an amount of the deviation ΔΦ, obtaining the backplating vector VBP from a difference between the grid voltage control parameter VG(k+1) and the developer bias control parameter VB(k+1), and performing operation (f);
• (f) repeating operation (e) if the backplating vector VBP is smaller than the minimum critical value VTmin, and repeating operations (a) through (e) if the backplating vector VBP is greater than the minimum critical value VTmin;
• (g) increasing the control parameter “a” by the increment “α”, setting the developer bias and grid voltage control parameters VG(k+1) and VB(k+1) based on the amount of the deviation ΔΦ, obtaining the backplating vector VBP from a difference between the the developer bias and grid voltage control parameters VG(k+1) and VB(k+1), and performing operation (h);
• and
• (h) repeating operation (g) if the backplating vector VBP is greater than a maximum critical value VTmax, and repeating steps (a) through (g) if the backplating vector VBP is smaller than a maximum critical value VTmax.

A method of compensating for image quality of a printing machine having a color toner density sensor receiving light reflected from test patches having different toner area coverage and converting the received light into a toner reproducing curve (TRC) value to control a developer bias and a grid voltage, the method comprising:

• comparing the TRC value with a target TRC to obtain a deviation;
• comparing the deviation with a reference value;
• calculating a developer bias control parameter and a grid voltage control parameter from a measured developer bias, a measured grid voltage, and the deviation;
• calculating a backplating vector from the developer bias control parameter and the grid voltage control parameter;
• comparing the backplating vector with a second reference value;
• and
• determining the developer bias control parameter and the grid voltage control parameter as new control parameters to control the developer bias and the grid voltage when the backplating vector is greater than the second reference value.