AUTOMATED FLUIDIZED BED GRINDER
Original Publication Date: 1993-Aug-31
Included in the Prior Art Database: 2004-Apr-06
Xerox Disclosure Journal
Disclosed is an automated process control system for use in fluidized bed grinder process equipment for controlling toner particle size properties. The system enables particle size process control to be improved beyond that achievable by human operators monitoring control charts. The system provides improved process capability in grinding operations, improved product quality and yields. Consistently "on spec" or centered particle size properties of the ground toner enables optimization of subsequent unit operations, such as classification, thereby increasing yields and throughput. Current particle size process control schemes require human monitoring of control charts for grinder process parameters (wheel speed and air flow) and for quality control of particle size parameters such as Volume Median Diameter. For micronization, there are known process control variables of VMD: wheel speed, air flow, equipment wear, and raw material variations. Wheel speed and air flow are process parameters used to center or set toner VMD. The number and sophistication of control chart monitoring criteria and process parameter adjustment algorithms are limited by a need for simplicity and speed of operator activities. By automating these tasks, the system can perform more sophisticated criteria testing and adjustment algorithms, and also, guarantee timeliness and accuracy. This allows the operator to watch for the non-routine occurrences that the system is not allowed to compensate or correct for on its own. Enablers for a fluidized bed grinder "Closed Loop Control" process are: 1) access to synchronized quality control process data; 2) criteria for detecting mean level shifts; 3) understanding of process equipment operating curves; and 4) access to output set point changes to equipment control system. Using these enablers, software is adopted to monitor quality control data for mean level shifts and to adjust the process to center the product specification quality control data, when appropriate.