Design of a Sensor System for On-Line Monitoring of Contact Pressure in Chalcographic Printing

Abstract

Key Answers

What is a chalcographic printer?

A chalcographic printer is a type of press used to transfer ink from an engraved metal plate onto paper, essential in printing processes requiring high precision, like currency production. This system relies on contact pressure for image transfer.

What are the challenges in monitoring contact pressure in chalcographic printing?

Current chalcographic printers lack on-line contact pressure monitoring, requiring machines to be shut down for static assessments. This creates inefficiencies and can compromise the consistency of high-quality impressions over time.

How does the sensor system designed in this paper improve printing quality?

The proposed sensor system includes an on-line strain gauge-based load cell that monitors roller pressure during printing. This setup ensures precise, real-time adjustments, reducing errors, waste, and enhancing alignment for consistent print quality.

How does temperature control affect printing quality in chalcographic presses?

The sensor system includes a temperature control module to keep the plate at an optimal 80°C. This control is critical for ink performance, especially since ink viscosity and adherence are temperature-sensitive.

What benefits does on-line pressure monitoring offer for industrial printing?

On-line pressure monitoring enables uniform roller alignment, reduces material waste, minimizes machine downtime, and helps maintain long-term consistency in print quality. This approach also ensures reproducibility despite environmental variations.

Abstract

Chalcographic printer is the name given to a specific type of press which is used to transfer the printing of a metal-based engraved plate onto paper. The printing system consists of two rollers for pressing and carrying a metal plate onto which an engraved inked plate is placed. When the driving mechanism is operated, the pressure exerted by the rollers, also called contact pressure, allows the engraved image to be transferred into paper, thereby obtaining the final image. With the aim of ensuring the quality of the result, in terms of good and even transfer of ink, the contact pressure must be uniform. Nowadays, the strategies utilized to measure the pressure are implemented off-line, i.e., when the press machines are shut down for maintenance, which poses limitations. This paper proposes a novel sensor system aimed at monitoring the pressure exerted by the rollers on the engraved plate while chalcographic printer is operating, i.e., on-line. The purpose is two-fold: firstly, real-time monitoring reduces the number of breakdown repairs required, reduces machine downtime and reduces the number of low-quality engravings, which increases productivity and revenues; and secondly, the on-line monitoring and register of the process parameters allows the printing process to be reproducible even with changes in the environmental conditions or other factors such as the wear of the parts that constitute the mechanical system and a change in the dimensions of the printing materials. The proposed system consists of a strain gauge-based load cell and conditioning electronics to sense and treat the signals.