Abstract: Digital circuitry and microprocessor techniques are used to monitor the quality of toner operations in a copier and take appropriate corrective action based upon the monitoring results. Patch sensing is used. Reflectivity signals from the patch and from clean photoconductor are analog-to-digital converted and a plurality of these signals taken over discrete time periods of a sample are stored. The stored signals are averaged for use in determining appropriate toner replenishment responses and/or machine failure indicators and controls.

Abstract: Control system which measures overshoot or undershoot time of a controlled variable with respect to a set value and adjusts a proportional count if the overshoot or undershoot time period exceeds fixed values. The proportional count is used to control the system output in a proportional manner, such as supplying k out of every n cycles of power, where k represents the proportional count. To prevent excessively long periods of overshoot or undershoot, an overlimit detector provides adjustments of the proportional count when the overshoot or undershoot measured time exceeds an overlimit value.The control system has general applicability but is described in the temperature control of a fuser hot roll such as used in electrophotostatic copiers.

Abstract: Copier fuser roller temperature is monitored during the warm-up period by a series of decreasing temperature threshold levels. Each threshold level is monitored for a preselected time period and reduced for the next time period. The sampling continues until the fuser roller temperature sensed by a thermistor or the like exceeds the threshold level. At that point, the control logic for the copier is enabled for normal copying since the fuser roller temperature profile is then approaching at an adequate level for proper fusing of copy sheets. Fuser over-temperature, under-temperature and failure conditions are determinable.

Abstract: System and method for determining whether a first operation is responsive to a controller. A second operation, whose successful functioning depends on the successful functioning of the first operation and which produces a sensible result, is initiated while the first operation is inhibited by the controller. Sensing that the second operation is producing a result indicates that the first operation is not responsive to the controller. A further test is provided to determine whether the second operation is functioning properly.