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DESIGN AND ANALYSIS SOFTWARE DELIVERS ACCURATE DRUG DOSE- PAPER AT NAFEMS CONFERENCE SHOWS HOWMANUFACTURING TOLERANCES CAN BE CONSTRAINED
It is important for many devices - particularly drug delivery devices in the medical industry - that they can be produced accurately and that they operate correctly. A paper at the recent NAFEMS (National Agency for Finite Element Methods and Standards) conference showed how a combination of techniques and software can ensure such devices are produced consistently and operate reliably, so as to deliver a precise dose every time.
The paper was presented by Ray Ellender and Rod Giles of stress analysis consultant Elite Consulting. It described how they used several software packages to pull together different elements to create a robust design for a drug delivery device.
Elite used the Mechanism Dynamics Option in Pro/ENGINEER®, Sigmetrix CETol® and Pro/ENGINEER MECHANICA®.
An initial prototype design was produced in Pro/ENGINEER® and because this is a mechanism, the first step was to use the Mechanism Dynamics Option (MDO) in Pro/ENGINEER to analyse the kinematics and dynamics of the mechanism.
Once this had been completed using nominal dimensions, an initial assessment of likely materials and manufacturing process was made and tolerances were added to the parts, based on default tolerances. The next step was to analyse the effect of tolerances on the performance of the device.
To do this a 3D statistical tolerance package from Sigmetrix called CETol® was used. This takes in the nominal dimensions directly from the CAD model and then tolerances and manufacturing process capability are added to the relevant dimensions and both a statistical and worse case tolerance analysis are performed.
The results from this analysis showed not only whether the device would remain in specification throughout the tolerance range but also which tolerances showed the greatest contribution and sensitivity. Armed with this knowledge, targeted improvements to the design were made.
However, because part of the design relies on the flexibility of a spring component, a further step was necessary. This was to conduct a finite element analysis of the spring, not only to achieve the right stiffness and an acceptable stress with the nominal design but also to assess how stiffness and stress might vary with tolerances of the spring’s manufacture.
Pro/ENGINEER MECHANICA® software was chosen for this part of the analysis because of its ability to conduct sensitivity and optimisation analyses.
The results from these various analyses were then reviewed and design iterations made, knowing which aspects were likely to yield the biggest improvements because the sensitivities to the various variables were known.
Ray Ellender, Managing Director of Elite Consulting, explained: “Using this methodology a robust design was produced that was relatively insensitive to variations in the production processes.”
He added: “We were delighted to be invited to speak at such a high level industry event as the NAFEMS UK conference. It provided the perfect forum for those involved in computer aided design engineering and structural analysis to see how the latest industry innovations, including Pro/MECHANICA and CETol, can be used to obtain optimum results.”
Long AbstractTo download the long abstract, click here PresentationTo download the presentation that was given at the conference, click here. How Can Elite Help YouTo find out how we
may be able to help you with mechanism analysis, stress analysis, tolerance
analysis, or anything else, please contact us by going to our Contact Page
END Notes to editors
1. Elite Consulting is a specialist stress analysis consultant based in Northampton. It is a provider of computing for design analysis, new product design and project management software and services. Elite Consulting is also a software reseller of CETol, PD-Trak and a Pro/Engineer trainer specializing in Pro/Engineer Mechanica. 2. NAFEMS (The National Agency for Finite Element Methods and Standards) was formed in 1983 to promote the safe and reliable use of finite element and related technology. It is a not for profit global membership organisation. For more information visit www.nafems.org/ 3. The NAFEMS UK Conference was held at the Paramount Cheltenham Park Hotel in June 2008 and aimed to increase awareness and provide a discussion forum for topics important and relevant to engineering industrialists and academics. Entitled “Engineering Simulation: Effective Use and Best Practices”, the conference gave delegates an independent insight into current best practice and the state-of-the-art in finite element analysis (FEA), computational fluid dynamics (CFD) and associated technologies, providing a comprehensive overview of the technology available. 4. The agenda included ‘hot topics’ and best practices in the simulation world aimed at analysts, engineers, team leaders and managers responsible for ensuring fit-for-purpose engineering using modern simulation software. A series of high level presentations over the two day conference included one from Elite Consulting.
Illustration caption:
This hand-held drug delivery is designed to deliver a self-administered precise dose of medication. It is operated by the patient turning the handwheel through one revolution. The handwheel serves as a crank connected to a conrod which in turn is connected to a piston. The piston slides in the main body of the device freely until it contacts another piston. Once it makes contact, the 2 pistons move in unison and the movement of the first piston delivers the dose. Behind the second piston is a spring and this serves to give ‘feel’ to the device, so that the patient can tell when the drug is being delivered. The important features are that the piston moves the correct distance and that the spring has the right characteristic, for correct feel.
Due to the restrictions imposed by client confidentiality, what is shown here is an idealised representation of such a device, which shows the principles that were used but not the actual design.
For further information contact:
Ray Ellender Elite Consulting Ltd Tel: 01604 830886
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