Duplex Sheet Registration via Real-Time Skew Measurement
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Solution Overview
Problem
Conventional sheet registration systems in high-speed printers face challenges in accurately aligning duplex images due to improper sheet size, which leads to misalignment of images on opposite sides of the sheet during the duplex printing process, especially when the sheet is non-rectangular or of incorrect dimensions.
Innovation Solution
A sheet measurement system comprising a nip assembly with nip parameter sensors and sheet sensors, connected to a microprocessor, which determines the sheet's dimensions and adjusts the image areas on both sides to ensure symmetry and accurate alignment, using drive rollers and idler rollers to correct skew and lateral offset errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional sheet registration systems are used for duplex printing, then the printing process can be completed, but images on opposite sides of the sheet become misaligned due to improper sheet size
Solution Approach 1:
The system performs preliminary measurement of sheet dimensions and skew angle using sensors before the duplex printing process begins. The controller calculates corrected image areas based on these measurements, allowing the registration system to compensate for improper sheet size and shape before images are printed, thereby ensuring accurate alignment.
Solution Approach 2:
The system uses sensors to detect actual sheet dimensions and skew angle, feeds this information back to the controller, which then adjusts the image area definitions accordingly. This feedback loop enables the system to adapt to varying sheet sizes and maintain precise image alignment throughout the duplex printing process.
2Productivity
If the sheet is non-rectangular or of incorrect dimensions, then the sheet can still be processed, but the first and second image areas cannot be properly aligned
Solution Approach 1:
The system dynamically adjusts the definition of first and second image areas based on real-time measurements of sheet skew angle and dimensions. Rather than using fixed image areas, the controller calculates adjusted image areas that adapt to the actual sheet geometry, enabling accurate duplex printing even with non-rectangular or incorrectly sized sheets.
3Measurement precision
If active registration systems correct for skew and lateral offset, then sheet alignment is improved, but the system cannot compensate for improper sheet size
Solution Approach 1:
The system changes the parameters defining the image areas based on measured sheet characteristics. The controller calculates corrected image areas by adjusting both the position and dimensions of the image areas according to the measured skew angle and sheet dimensions, thereby compensating for improper sheet size while maintaining alignment precision.
Data Source
AI summary
A registration and measurement system for a printing machine includes two drive rollers and two opposing idler rollers. Each drive roller and idle roller combination respectively form a drive nip. A single servo or stepper motor is operably connected to the drive rollers through a gear train, allowing the motor to drive the sheet feeding nips. A rotary encoder is attached to each idler roller. Optical sensors are provided above a desired sheet path. The optical sensors and the rotary encoders are connected to a controller and are operable to deliver output signals to the controller. The controller is operable to determine the length of a sheet passing through the nips based upon the signals received from the optical sensors and the rotary encoders.