Abstract: According to a feature of the present invention, an imaging apparatus has a support with a cylindrical inner surface for receiving a recording media about an axis of the support. A rotor forms a gap with the inner surface such that the gap varies as the rotor rotates and as an inverse function of the concentricity of the support and the rotor. An electrode is carried at the portion of the rotor forming the gap with the inner surface such that a capacitance between the electrode and the inner surface varies as the rotor rotates and as an inverse function of the concentricity of the support and the rotor. A detector, including a power source adapted to produce an electrical charge across the gap and an impedance, measures the change in the dimension of the gap as the rotor rotates so that the concentricity of the support and the rotor can be measured while the rotor is rotating.

Abstract: Apparatus for estimating LED printhead junction temperature as a function of an input data stream, and for automatically compensating the printhead drive signal to maintain proper printer calibration to provide junction-level compensation for efficiency loss of an LED as the LED warms due to thermal energy generation from an electrical drive current is effected by a plurality of selectable LED temperature-specific look up tables constructed for a plurality of different LED temperatures. The selected look up table produces an output for driving the LED when the selected look up table is accessed by the input data. A model of the thermal characteristics of the LED, its heat sink, and the structure attaching the LED to the heat sink is adapted to produce an estimate of the temperature of the LED as a function of the image data. An address decoder selects one of the plurality of look up tables to process the input data stream in accordance with the estimate produced by the model.

Abstract: A printhead includes a plurality of recording elements such as LEDs each having a light output characteristic related to a driving parameter such as current. A plurality of driver circuits establishes the driving parameter for driving the recording elements. The driver circuits are mounted on a circuit board. A flex circuit having a conductive pattern electrically connects the driver circuits to the recording elements. The driver circuits include resistors for use in regulating the driving parameter. In lieu of mounting the resistors on the circuit board, the resistors are instead advantageously mounted on the flex circuit for controlling current to the respective recording elements. This allows the resistors and recording elements to be replaced without the need to also replace or modify the circuit board in the event that more efficient recording elements are to be used.