Boxing clever

A two-year Ministry of Agriculture Food and Fisheries research project is looking at the traditional design process of the packaging industry.

Most packaging machines are created as a result of the direct working experience of their designers, and evolve in response to the demands of their users. Many have reached the point at which increases in product variation, throughput and quality can no longer be met.

Before embarking on a major program of design improvements, a company needs to know whether any significant capability remains in the current design, or if a radically different approach is required.

In order to improve a machine, it is necessary to obtain a basic understanding of its processes and a knowledge of its use. This understanding is acquired through detailed modelling, analysis and assessment of the machine system. The University of Bath addresses these tasks by utilising high-speed video techniques and constraint based modelling, as well as interacting with the company. The constraint-based analysis uses software created at the university, and Kodak and the Process and Packaging Machinery Association (PPMA) provide the high-speed equipment.

The video analysis observes individual operations and measures motion characteristics. This process identifies the process times and an understanding of machine/process constraints. It also provides a mechanism for the validation and testing of the machine system models. This allows the geometry to be constructed and the constraints that govern their interactions to be specified. In the early stages these rules may not be fully appreciated and are only incorporated into the model as the process advances.

At a low level the constraint rules are used to specify how the various links are to assemble. At a higher level, they indicate restrictions imposed on conditions such as velocity, acceleration and jerk. In this way it is straightforward to build up a model of a mechanical system and then simulate and analyse the motions.

Once the constraints are understood and a representative model has been constructed, incremental changes, elemental (sub-assembly) redesigns or radical (process/system) redesigns can be evaluated. Analysis techniques can show whether the machine is meeting its potential, is susceptible to failure, or whether any changes would make it more difficult to set-up or run reliably. Suitable redesigns are proposed and assessed in close consultation between the partners concerned.

Assessment and identification of pertinent dynamic effects is being undertaken by Imperial College whilst dynamic FEA is performed by Fraser-Nash Consultancy. During the 18 months the project has been running, the redesign approach has been applied to a number of packaging machine manufacturers, and in each case has involved close collaboration between the technical partners and the design teams.

The methodology has demonstrated that improvements in machine performance can be achieved by the respecification or redesign of individual components and/or sub-assemblies. It has also found that a number of the machines are approaching their performance limits. This suggests that major changes in performance can only be achieved by equally major changes in operating principles.

The methodology is being generated to integrate the practical skills, design knowledge and experience of the company’s design team with the analysis, modelling and design theory of the technical partners. This provides a framework for the creation of the next generation of packaging machines which assimilates the modelling techniques available for R&D and the wealth of design experience inherent in the packaging industry.