Preform Length Sensing for Accurate Stretch Blow Molding
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Solution Overview
Problem
Existing container manufacturing processes face issues with preform shrinkage during heating, leading to inconsistent stretching and potential damage or poor quality due to variations in preform length and diameter, which current automation systems cannot correct.
Innovation Solution
A method involving real-time measurement of preform length after heating and adjustment of the elongation rod's impact position based on these measurements, using non-contact imaging and electronic processing to ensure accurate stretching and blowing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If preforms are heated to transform them into containers by blow molding, then the material becomes sufficiently pliable for deformation, but the preform undergoes shrinkage causing length reduction and diameter increase which leads to inconsistent stretching and potential damage
Solution Approach 1:
The patent applies preliminary action by measuring the preform dimensions (length and diameter) immediately after heating but before the stretching operation. This measurement data is then used to adjust the stretching parameters in advance, compensating for the thermal shrinkage that occurs during heating. The system calculates the actual stretching force and rod position needed based on the measured dimensions, ensuring consistent container quality despite dimensional variations caused by heating.
2Productivity
If the stretching rod is positioned to accommodate average preform dimensions, then the process can run continuously, but preforms with varied dimensions suffer from excessive cooling or perforation damage
Solution Approach 1:
The patent implements dynamics by making the stretching rod position and stretching force adjustable based on real-time measurements of each preform's dimensions. Instead of using a fixed position suitable for average preforms, the system dynamically adapts the stretching parameters for each individual preform. The control system modifies the rod's starting position and the force applied during stretching according to the measured length and diameter, preventing both excessive cooling (which occurs when the rod starts too early) and perforation damage (which occurs when too much force is applied).
Solution Approach 2:
The patent applies feedback by using sensors to measure the actual dimensions of each preform after heating and using this information to adjust the stretching parameters. The measurement system provides feedback about preform length and diameter variations, and the control system uses this feedback to calculate and apply the appropriate stretching force and rod position. This closed-loop control ensures that each preform is stretched according to its actual dimensions, maintaining reliability while allowing continuous production.
3Manufacturing precision
If automated measurement and adjustment systems are implemented to correct preform dimension variations, then manufacturing precision improves, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical adjustment systems with electronic measurement and control systems. Instead of using multiple adjustable mechanical components to compensate for preform dimension variations, the system uses optical or electronic sensors to measure preform dimensions and electronically controls the stretching rod position and force. This substitution of mechanical systems with electronic/measurement systems achieves high manufacturing precision while keeping the overall device complexity manageable through software-based control algorithms.
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
Improves container quality by aligning the stretching process with actual preform dimensions, reducing defects and maintaining production efficiency while minimizing waste.
Implementation Method 1
The preform is therefore first thermally conditioned by circulating it within a heating station. The heating station includes heating elements such as infrared lamps.
Implementation Method 2
The heating station includes heating elements such as infrared lamps.
Implementation Method 3
Pressurized gas is also introduced into the preform to transform it into a container by blow molding.
Implementation Method 4
Stretching and blow molding (or pre-blowing and blow molding) allow the material constituting the preform to undergo molecular bi-orientation, which gives the final container specific mechanical properties.
Implementation Method 5
The forming operation includes a stretching (also called elongation) step of the preform, using an elongation rod that is attached to the mold and slides down towards the bottom of the mold.
Data Source
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AI summary
The invention relates to a method for controlling a method for forming preforms (12) made of thermoplastic material, the forming method comprising: - an operation of heating the preform (12); - an operation of introducing the preform (12) into a mould (36); - a stretching operation consisting in moving an elongation rod (46), the elongation rod (46) passing through a position (PO) of impact with a bottom (18) of the preform (12); the control method being characterised in that it comprises: - a step (El) of measuring the length (L) between a neck (16) and the bottom (18) of a preform (12), performed after the heating operation and before the operation of introduction into the mould (36); - a step (E2) of adjusting the impact position (PO) of the elongation rod (46) on the basis of a measurement of the length (L) made during the measurement step (El).