Mechatronic design exploration for wide format printing systems

This work aims at increasing the performance of Wide Format Printing Systems (WFPS) via a mechatronic approach. With increasing performance is meant that one or more of the categories: productivity, print quality, reliability and/or cost of production, is improved without sacrificing one of the others. Although the main focus lies on WFPS, the methodology in this work can be extended to a wider class of printers or to other applications. Multi-printhead scanning inkjet configurations are considered where each printhead contains hundreds of nozzles. This work mainly concentrates on positioning of the 6 degrees of freedom of all printheads in time and space. Questions about what happens inside the nozzles will not be addressed. However, the macroscopic characteristics of the droplet formation process are taken into account, such as jet speed, jet timing and temporary nozzle congestion. A concept exploration is carried out, including a productivity analysis and a printing accuracy analysis focussing on mechanical design parameters. Both analyses are set up in a generic way such that they can be applied to other printer configurations or to a wider range of applications. Based on this analysis, two concepts are chosen to be investigated further. The first concept is active printhead alignment. Instead of putting all effort and cost in reduction of the manufacturing tolerances to obtain an accurate printhead alignment for higher productive WFPS, the misalignment of each printhead is measured and actively controlled. A low cost sensor, actuator, and alignment mechanism are developed to achieve this. An experimental setup is built to validate this concept. The concept has been shown to be feasible satisfying the accuracy specification of less than 10 µm. Moreover, this concept enables several extensions, such as (i) adding redundant printheads which take over printing for temporarily congested nozzles, (ii) staggering of printheads in paper transport direction or even distribute the printheads over multiple carriages which would be infeasible for fixed printheads due to thermal effects and parasitic dynamics. The second concept is a new carriage drive design for higher productive WFPS. A productivity increase can be achieved by increasing the amount of effectively printing nozzles and increasing the jet frequency. As a result, the carriage will be heavier due to the addition of printheads and the carriage speed will need to be increased due to the higher jet frequency. A doubling in mass and speed results in an actuator power increase by a factor of 16 for the case that the effective relative printing time is kept equal. Scaling of the drive in conventional WFPS is therefore expensive and energy inefficient. As an alternative, an energy buffering drive concept is developed which stores the kinetic energy of the carriage in a spring and returns this energy to the carriage in the opposite direction. This way, only a small additional carriage drive is required to overcome friction forces acting on the carriage while moving at a constant speed. To validate this concept, an experimental setup is built. The concept has been shown to be feasible. However, the prototype has to be engineered further to make it simpler such that it becomes cheaper in comparison with an equivalent conventional WFPS where the drive motor has been upscaled. The mechatronic design of both concepts focus on a much higher performance than conventional WFPS. The results are innovative designs which are easier scalable than conventional methods and enable new features which would not be possible by scaling conventional WFPS.