Liquid ejection apparatus, liquid ejection method, and printing system

What is this patent about?

’654 is related to the field of liquid ejection apparatuses, such as inkjet printers, that utilize multiple drive signals to achieve varied droplet sizes. In high-resolution printing, it is necessary to eject droplets of different volumes—large, medium, and small—to produce high-quality gradations. Traditionally, this required either a complex array of unique drive signals for every possible droplet size or a single complex signal that limited throughput, often leading to hardware complexity or increased susceptibility to signal noise.

The underlying idea behind ’654 is a dual-layer selection mechanism that expands the variety of available ejection pulses without increasing the number of physical drive signal lines. Instead of relying on a one-to-one mapping between a drive signal and a droplet size, the system generates two primary drive signals, each containing multiple waveform sections. By first selecting one of the two main signals and then sub-selecting specific pulses within that signal, the inventor realized that a wide range of droplet volumes could be achieved using minimal hardware resources.

The claims of ’654 focus on a control architecture that uses logic gates to prevent electrical conflicts between the two drive signals. Specifically, the independent claims describe a controlling section equipped with a first and second switch, a memory for selection data, and a pair of AND gates. One AND gate receives a direct drive selection signal while the other receives an inverted version, ensuring that the two switches are mutually exclusive. This hardware-level interlock ensures that only one drive signal can be connected to a piezoelectric element at any given time, even if the control data is corrupted.

In practice, the invention functions as a fail-safe multiplexer for high-voltage pulses. The drive signal generation section continuously produces two distinct waveforms, COM_A and COM_B, which are distributed to all nozzles. The local controller at each nozzle uses the AND gate logic to act as a gatekeeper. If the selection data indicates that a small dot is needed, the logic automatically disables the switch for COM_A and enables the switch for COM_B, allowing only the specific sub-sections of COM_B required for a small droplet to reach the actuator.

This approach differs from prior solutions by moving the safety logic from software to a hardware-integrated mutual exclusion circuit. In typical carriage-based printers, long flexible cables are prone to electromagnetic interference, which can flip bits in the selection memory and accidentally trigger both switches simultaneously, potentially damaging the print head. By using the inverted signal logic at the AND gates, ’654 ensures that an error in the selection data cannot cause a short circuit between the two drive signal lines, providing a robust defense against signal noise while maintaining high-speed gradation control.