Developing a 12 m Wide Printer With LabVIEW and CompactRIO

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"LabVIEW and the CompactRIO system provide excellent integration of I/O, image processing, and engine control as well as a lot of flexibility during the development process."

- Udo Schwadtke, Technische Universität Berlin

The Challenge:
Developing a 12 m wide printer to prepare and print cotton material.

The Solution:
Using LabVIEW and cRIO-9024 starting with the development process all the way through to the finished product.

Author(s):
Stephan Cepek - Big Image Systems Deutschland GmbH
Udo Schwadtke - Technische Universität Berlin

About Big Image

Big Image Systems Deutschland GmbH provides digital large-scale printing on flexible materials, such as cotton fabric, using piezo technology. Our experience in technical, craft, and artistic contents helps us to develop methods and services to find a base for every idea. This opens up a variety of possibilities for creating a viewing experience. Our products are used in theaters, exhibitions, museums, TV studios, trade shows, and events. Our clients come from all over the world.

Motivation

The printers on the market feature a printing width of up to about 5 m. Besides paper and foil, cotton is a form of print media. Cotton materials are manufactured in fabric panels with a width of up to 12.5 m and a length of up to 60 m. This triggered Big Image Systems’ idea to print on the full available fabric width. Because the material cannot absorb compression forces and exhibits a strong nonlinear behavior, the handling is difficult and becomes even harder with increasing width. Delivered in bales on a Euro-pallet, the fabric has to be aligned and coiled on a truss prior to printing on it. Because of the size and the difficult handling of those large fabric panels, aligning them requires extensive work. 

Cooperation with the Technische Universität Berlin

The system was developed in cooperation with the Technische Universität Berlin.

One System Becomes Two

Based on practicality, the printer consists of two systems. The first system features an over 12 m wide rotating drum on which the fabric is mounted during the printing process. In front of the drum is an appropriately long linear actuator with the printer carriage that finally transfers the color onto the material.

The second system deals with the preparation of the fabric for the printing process. This second part, the aligning system, was developed and implemented with the help of NI products. Both system parts can process theoretically endless fabric panels. Practically, however, the length is limited to about 60 m by the manufacturer.

Structure of the Aligning System

The aligning system consists of two parts. The upper part forms the mounting structure for a roller system driven by 15 electric motors to manipulate the fabric. The lower part consists of a long linear actuator to move a line scan camera, two 2-axis grippers to guide the fabric on the sides, and an automatic winding machine for the material. The upper part is height-adjustable through two electric motors so that the fabric can be conveniently inserted into the system.

The electrical components are situated in two control cabinets. The first cabinet includes the Windows host PC and a CompactRIO system. The Windows PC is responsible for the CPU-intensive image processing of the images delivered by the line scan camera and the two area scan cameras. The I/O communications with all the sensors and actuators as well as the aligning processing logic are managed by the CompactRIO system. The second cabinet contains most of the power electronics, including one Bosch and 23 Kollmorgen drives.

Image Processing System 1—To insert the fabric in a defined way into the system, the edges of the fabric are guided by two 2-axis grippers, one on the left and one on the right. During this process, the stretch of the fabric is measured by the area scan cameras and adjusted by the grippers according to precise specifications.

Image Processing System 2
—To align the fabric absolutely straight and right angular, a second image processing system is used. For this process, a line scan camera is mounted on a linear actuator. It slides underneath the fabric and takes a seamless picture over the complete material width. The image uses, depending on the width of the material, up to 500 MB memory. Both image processing methods were developed with the support of the NI vision library. This way, the developed software can follow one individual thread from the 12 m long picture and therefore determine the thread position very accurately. Depending on the type of material, the thread can have a width of only 0.7 mm.

Actuator System—The actuator system consists of 24 electric engines. They have different roles such as fabric transport, fabric manipulation, and movement of the line scan camera. The control of these engines is quickly and easily implemented through the EtherCAT protocol with help of the LabVIEW SoftMotion Module.

LabVIEW

The architecture of the LabVIEW program consists of two main programs. The first program runs on the CompactRIO system. In addition to a loop to receive network commands from the host PC, it contains a state machine that displays the sequence of the alignment process. The second program is performed on the host PC and displays the user interface. Here, the operator can configure various parameters such as type of material, width of material, and speed. Also, different support-tools for the alignment process can be accessed, and important system parameters can be displayed. The host program consists of multiple loops that are responsible for sending commands to the CompactRIO system, activating the linear actuator, and processing images for the area and line scan cameras. The recording of the images with the line camera and their processing are also implemented with the help of a state machine.

The system is rather large and causes a lot of extra effort for the developer in terms of movement; therefore, a practical Android app to remotely control the aligning system via Bluetooth is used.

Conclusion

During the phase of development, LabVIEW was used in many cases to successfully implement trial structures quickly and flexibly. Often, various solution principles had to be developed and tested for the described functions. Furthermore it is very easy to improve the program structures or implement new hardware if it is necessary, even now where the basic production process is working.

Among others, especially LabVIEW helped us to develop a solution to offer seamless, large format prints on flexible fabric. The afterwork costs were reduced greatly (seamless prints) and the customers are now able to store our products without a loss of quality (flexible fabric). Additionally we invented new print-products with this technology to extend our assortment.

Author Information:
Udo Schwadtke
Technische Universität Berlin
Müller-Breslau-Straße 8
Potsdam 14482
Germany
Tel: +49 (0)30 31424666
udo.schwadtke@tu-berlin.de

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