Hot-Stamping Machine Retrofit to Improve the Production of Decorated Plastic Bottles

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"Having flexible tools such as NI hardware and software is an incentive to justify investing in applications development that in the past seemed an insurmountable vulnerability."

- Erwin Franz Rodriguez, Erlab SA de CV

The Challenge:
Reuse the chassis of an out-of-service hot stamping machine to build a modern bottle decorating machine at an accessible price.

The Solution:
Implementing a machine vision system based on a 1742 smart camera measures displacement errors in plastic bottles and sends the corrected coordinates to a servo stamping system to decorate within .2mm of precision up to 36 bottles per minute.

Author(s):
Erwin Franz Rodriguez - Erlab SA de CV

Introduction:

 

The CER E001 bottle-decorating machine is a discontinued model designed in France by the company CER-ITW, with few possibilities for spare parts or repairs. It was decided to update the existing, out-of-service machine given that the new models are costly and lack the functionality requested by the final user.

 

Application Description:

In recent years, it has become common practice for Mexican companies to acquire replacement machinery from other countries. Important production processes are often running with machines that are mostly outdated, require maintenance, do not have available replacement parts, and represent a monetary risk in the absence of solutions to address stoppages or unexpected failures.  The plastics industry and its transformation has had sustained growth that has generated many new providers who dramatically increased the competitiveness of the sector. Add-ons to plastics products, such as hot-stamping decoration, are becoming the differentiating factor for many companies. 

Hot-stamping is a thermal transfer printing technique. A foil is placed between a mold with a stamping relief and the piece to be decorated. The foil has a high-resolution pigmentation which is transferable if the temperature of the plate (mold) is in the range of 100 to 300 degrees Celsius.  This temperature is determined by considering the stamping area, foil type, stamping time and the normal force between the object to be decorated and the mold. Although it is currently one of the more effective processes to decorate plastic cylinders, few companies can offer this option to customers due to the complexity of ensuring repeatability in printed patterns, the input costs, and the production time of this process. The accuracy of the location and printing quality are often negatively impacted when the production rate is increased.

To solve this problem, the plate´s position is controlled by two servomotors coupled with 2 high precision ball screws. In order to allow the double axis plate system to stamp each cylinder correctly, the piece to be decorated and the plate should start always at the same distance.  Additionally, the piece to be decorated must be located at a fixed vertical distance from the plate that guarantees the required normal force needed for a correct stamping. If the prints need to be longer than the contact surface between the cylinder and the plate, it is required for the piece to rotate simultaneously with the displacement of the plate during stamping. The iron temperature, distance, speed rotation of the cylinders, and the speed of the horizontal movement of the plate are equally important to ensure successful hot-stamping.

Considering the above, a four arm indexing table was refurbished and placed in the center of the machine. This indexing table has four main positions: feed station, machine vision inspection station, stamping station, and product release station. A stepper motor is assembled to each arm of the indexing table. Each motor is coupled with a cylinder holder equipped with a pneumatic system to facilitate cylinder suction and expulsion. Most of the time hot stamping decoration is performed with cylinders already imprinted with some sort of image. Therefore it is a requirement for the machine to compensate for misalignment errors to prevent waste and assure the quality of the final product.

The misalignment compensation was achieved using a NI 1742 Smart Camera with LabVIEW Real-Time, executing a LabVIEW application developed with the Vision Development Module.

Executing machine vision functions, the application performs a misalignment measurement for precisely calculating the initial positions the stepping motor must have to sustain the piece and for the plate servomotors to execute the cycle at the desired user speed. In the case that the misalignment error does not allow the motion control system to achieve the calculated positions, the smart camera, through the OPC server, sends a signal to the system indicating a rejected piece, avoiding the execution of stamping in the next station and wasting material.  

This synchronization process required communication with the third party motion control hardware, in order to receive the coordinates obtained by the camera at a maximum of 120 ms. Thanks to the processing and I/O speed of the smart camera, to the efficiency of its real-time operating system, and to the OPC Server acquired with National Instruments, a stable system response time within the desired range was achieved.

 

Conclusion:

More and more manufacturers are beginning to consider the option of rehabilitating or upgrading their existing machinery to avoid negatively impacting the final cost of their product by purchasing new machines. Having flexible tools such as NI hardware and software is an incentive to justify investing in applications development that in the past seemed an insurmountable vulnerability.

Author Information:
Erwin Franz Rodriguez
Erlab SA de CV
Av Gustavo Baz No 3985. Tlanepantla, Estado de México
Mexico 54030
Mexico
erwinfranz@erlabtech.com

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