HP 4600 Service Manual - Page 172

Environmental change control (HP Color LaserJet 4610n and 4650 models) This control calibrates each bias to obtain the best image possible according to environmental changes. The environment conditions sensor detects the temperature and the humidity. The sensor sends this information to the DC controller in the form of the Temperature Detection signal (TEMSNS) and the Humidity Detection signal (HUMSNS). The DC controller monitors the environmental conditions of the printer based on these two signals. The DC controller controls the following biases to prevent image defects when it detects an environmental change. ■ Developing bias ■ Primary transfer bias ■ Secondary transfer bias If the environment sensor detects a temperature of below -30ºC (22ºF) or over 80ºC (176ºF), the DC controller determines this is an "environment sensor abnormality" and sends an error message to the formatter. Image density calibration control (DMAX) This control stabilizes image density by calibrating the values of the developing bias whenever one of the following events occurs: ■ When the printer is turned on ■ When a print cartridge is replaced ■ After a set number of pages have printed ■ When the formatter sends an operation command Image density calibration consists of three steps: 1 The DC controller forms density patterns for each color on the ETB by using varying levels of developing bias. 2 The color registration detection unit measures the image density of the density patterns that are formed on the ETB. 3 The DC controller uses the density measurements to adjust the developing bias to obtain he correct image density. 156 Chapter 5 Theory of operation ENWW