Direct Sensor Positioning for Sheet Speed Measurement in Printers
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Solution Overview
Problem
The existing printing apparatus faces challenges in achieving high-speed conveying and precise speed measurement due to the large space required by the speed sensor, leading to issues with ink discharge timing calculation, cockling of sheets, and sensor contamination by ink mist, which impede stable measurement and high-quality printing.
Innovation Solution
A printing apparatus configuration that includes a print head, upstream and downstream roller pairs, and a direct sensor positioned between the first and third roller pairs to measure sheet movement state, allowing for precise control of the print head and conveying mechanism, while minimizing the distance between the sensor and print head to prevent cockling and ink mist adherence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the speed sensor is positioned between the conveying rollers and the print head to enable high-speed conveying, then the printing throughput increases, but the distance between the sensor and print head increases causing the leading edge of the sheet to move upwards and contact the nozzles
Solution Approach 1:
The patent repositions the speed sensor from a location between the conveying rollers and print head to a location between the first and third roller pairs in the sheet conveyance direction. This spatial reconfiguration in the conveyance dimension allows the sensor to be positioned upstream of the print head while maintaining adequate distance, preventing sheet leading edge contact with nozzles while preserving high-speed conveying capability
2Length of moving object
If the distance between the speed sensor and print head is reduced to prevent sheet leading edge contact, then the sheet stability improves, but there is insufficient time to calculate speed and control ink discharge timing
Solution Approach 1:
The patent positions the speed sensor between the first and third roller pairs, which are upstream of the print head in the sheet conveyance direction. This preliminary positioning allows the sensor to measure sheet speed early in the conveyance process, providing sufficient time for speed calculation and ink discharge timing control before the sheet reaches the print head, while maintaining an appropriate distance to prevent sheet instability
3Length of moving object
If the distance between the print head and speed sensor is reduced to improve sheet stability, then the leading edge contact is prevented, but cockling affects the measurement position causing measurement error
Solution Approach 1:
The patent introduces the first and third roller pairs as intermediary elements between the print head and speed sensor. The sensor is positioned between these roller pairs, which act as mechanical reference points that stabilize the sheet during measurement. This intermediary positioning prevents cockling from affecting the measurement position while maintaining an appropriate distance from the print head
4Device complexity
If the print head and speed sensor are in close proximity without shielding, then the device complexity is reduced, but ink mist adheres to the sensor deteriorating detection signal
Solution Approach 1:
The patent positions the speed sensor between the first and third roller pairs, which serve as intermediary shielding elements. These roller pairs physically block ink mist generated at the print head from reaching the speed sensor, protecting the sensor's light emitting unit and photoreceptor without requiring additional shielding structures, thus maintaining detection signal stability
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
This configuration enables high-speed sheet conveying and precise speed measurement, maintaining high printing throughput and quality even during long operations by ensuring sufficient time for ink discharge timing control and preventing measurement errors and sensor contamination.
Implementation Method 1
A speed sensor (laser Doppler sensor) for directly measuring the moving speed of the sheet
Data Source
AI summary
An apparatus may include a print head, multiple roller pairs to convey a sheet, a direct sensor, and a control unit. The print head prints on a conveyed sheet. The multiple roller pairs nip the sheet at an upstream side of the print head to convey the sheet, nip the sheet at a downstream side of the print head, and nip the sheet at an upstream side of a first roller pair to convey the sheet. The direct sensor measures a surface of the conveyed sheet at a measurement position between a nip position of the first roller pair and a nip position of a third roller pair to obtain information relating to a movement state of the sheet. The control unit controls to correct at least one of driving control of the print head and conveying control of the sheet, based on the information obtained by the direct sensor.