Ernst Goepel

The ink drop sensor-a means of making ink-jet printers more reliable

An ink-drop sensor has been developed for use in ink-jet printers so that the function of the multinozzle printhead can be checked before printing starts or cyclically during printing. If the sensor detects that one or more nozzles have failed, the printhead can be restored to correct operation in a service station. This process, which is completely automatic and requires no intervention on the part of the user, increases the reliability of the ink-jet printer. The sensor principle utilizes the electrical conductivity of the ink. When ink droplets from any nozzle in the printhead are ejected onto comblike electrodes, conductive links are established between the prongs of these electrode combs, and changes in resistance can be measured at the sensor terminals. These changes in resistance are then converted in a signal-conditioning circuit into digital voltage signals. The author also discusses modified versions of the sensor suitable for special applications such as measuring the flight time of ink droplets and determining print position errors.<<ETX>>

Active RC networks: what benefit is there in having conjugate real zeros in the second-order transfer function?

The characteristics of a so-called real conjugate zero pair in the biquadratic transfer function are investigated and a new active RC network is provided to implement it. Different magnitude responses are obtained where the zero pair is varied while maintaining an invariant phase response. By this feature, the network can be seen as the counterpart to a phase shifter. With the aid of a simple additional circuit, the arithmetic transformation of a real conjugate zero pair into an imaginary conjugate, or into a double zero pair at the origin, is also demonstrated. This part of the network consists of operational amplifiers and resistors, each of equal value, which can be advantageously integrated. The result is an easy-to-design second-order filter section for multi-functional use.