Print Zone Encoder for Accurate Vacuum Belt Speed Measurement
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Solution Overview
Problem
In large industrial inkjet printers, the vacuum belt's friction and pulley wobble cause speed variations in the print zone, which are not accurately detected by traditional rotary encoders, leading to printing inaccuracies.
Innovation Solution
An encoder unit is positioned in the print zone to directly measure the vacuum belt's movement, using a rotary encoder connected to an encoder pulley, which provides feedback to the controller for precise speed regulation and ink timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rotary encoder is positioned at the drive pulley to measure belt speed, then the encoder structure is simple and easy to implement, but the measurement precision is insufficient because friction and pulley wobble cause speed variations that are not detected
Solution Approach 1:
An encoder belt is introduced as an intermediary element that directly contacts the vacuum belt in the print zone. This encoder belt transfers the motion of the vacuum belt to the encoder pulley, allowing accurate measurement of actual belt speed while isolating the encoder from the harsh vacuum environment and high-stress drive pulley conditions
Solution Approach 2:
The encoder system is positioned in a different spatial dimension (below the vacuum belt in the print zone) rather than at the drive pulley location. This dimensional relocation allows the encoder to measure belt speed at the critical print zone without being subjected to the same operational stresses and friction forces
2Manufacturing precision
If the vacuum belt operates under high vacuum forces to hold media flat, then the printing quality is improved, but the friction between belt and track causes speed variations that degrade measurement accuracy
Solution Approach 1:
The encoder belt serves as a mediator that measures the actual motion of the vacuum belt without being affected by the vacuum forces. It transfers the motion information from the high-stress vacuum belt to the low-stress encoder mechanism, enabling accurate speed measurement despite friction forces
Solution Approach 2:
The encoder belt is specifically designed to engage only in the print zone where accurate speed measurement is critical. This localized engagement ensures that speed variations caused by friction in the print zone are accurately detected, while maintaining the necessary vacuum forces throughout the entire belt loop
3Stability of the object's composition
If the drive pulley is subjected to substantial operating stresses to maintain belt tension, then the belt remains stable, but the pulley develops eccentric wobble that causes speed variations
Solution Approach 1:
The encoder belt acts as an intermediary measurement mechanism that is not subjected to the same substantial operating stresses as the drive pulley. It accurately tracks the vacuum belt motion without developing wobble, providing reliable speed measurements independent of drive pulley condition
Solution Approach 2:
The system compensates for pulley wobble by measuring actual belt speed at the print zone and using this information to adjust ink dispensing timing. This beforehand correction accounts for speed variations caused by wobble, maintaining printing accuracy despite pulley instability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system accurately measures and corrects for speed variations, ensuring consistent belt speed and improved printing accuracy by synchronizing ink dispensing with belt movement.
Implementation Method 1
The encoder unit also includes a pulley and a rotary encoder connected to the encoder pulley. The encoder belt wraps the encoder pulley to turn the pulley in response to the vacuum belt moving through the print zone. The rotary encoder connected to the encoder pulley gives feedback to a controller
Implementation Method 2
The encoder unit includes a belt that engages the vacuum belt in the print zone to transfer movement of the vacuum belt to the encoder belt
Data Source
AI summary
In one example, a system to support print media through a print zone in a printer includes an endless support belt, a driver to circulate the support belt through the print zone, and an encoder unit under the print zone to measure movement of the support belt in the print zone.