Identifying flaws and validating the mechanical characteristics of a design through physical prototypes and testing procedures can be a lengthy and iterative process for any design team. However, there are alternative testing and validation methods which can be used to reduce time, cost, and arguably provide more accurate results – before making the commitment to physical prototypes or tooling.
At HD, we were recently tasked with improving the functionality of a drug delivery device where we used simulation techniques, including FEA and SoildWorks Motion to significantly reduce development time. In one case, an injector design had been manufactured, and physically tested by our client. However, after reviewing test results and user feedback, they wanted to improve both functional performance and the user experience for the device. It was particularly important to optimise a clip engagement to ensure the device functioned correctly and provided sufficient tactile feedback to the user.
It is a costly and slow process to tweak a design and re-manufacture components to physically re-test and gather results. We were therefore tasked with not only redesigning the device, but also to verify the design prior to tooling manufacture. A key challenge of the brief was a narrow margin of changeable parameters which could be optimised to enhance the product’s performance.
We chose to use SolidWorks Motion as a tool for this brief because it’s focused on optimising the mechanical performance of mathematical CAD models. In this project, we used virtual springs, virtual motors and virtual body contacts to simulate the product in use. We were then able to quickly determine why and where changes were needed to enhance and optimise the performance of the design.
Motion can also be used for design validation where kinematic energy needs to be considered. For example, if we were designing a computer mouse and needed to know how much force it would take to move it 200mm across the desk. We would set up the models and input various parameters into the software and Motion can provide that information very quickly.
With the project in question, firstly, we replicated the existing mechanisms using Motion. By running a Motion study with the mathematical model, we were able to replicate data from the physical study which not only showed us that our mathematical models and Motion study were accurate but, gave us a benchmark to work from. When optimising the design of a critical clip interface, we could rerun the study and overlay the physical data for comparison. From here, our focus was to improve the product’s performance by decreasing the force required to operate it.
From this, we were able to iterate, retest, and develop a new and more effective design. Although the physical difference of the design change appeared relatively small, by using Motion testing, we were able to compare the original design’s performance against our new design.By using this method, changes could be made quickly by working within our SolidWorks CAD system. It’s relatively easy go into a 3D model, tweak it slightly and then run another study. It can be the case of minutes to make changes, rather than hours, or days. Whereas the alternative process of making a CAD change, then prototyping, setting up a test rig and then running tests to collate and analyse the results could take weeks per iteration to effectively gather the same results.
Whilst for this project, using Motion made up the bulk of our work, this tool can be utilised in many more projects with mechanisms than some design teams realise. FEA is already part of many designer’s utilities and applied frequently, however Motion is often overlooked. It’s highly versatile so can be used to validate early concepts, prototyping and again in the design optimisation stage too.
There are some limitations within Motion, but they can usually be overcome with a little lateral thought. For this project, the mathematical model was completely rigid, and we needed some flexibility to act as a clip feature. So, we worked around the limitation by creating a small joint and virtual spring in the area requiring flexibility. With a good understanding of mechanical design, there are usually work arounds to any software limitations.
After this theoretical work, an injection moulded component of the new design was manufactured and physically tested. This created a further set of results which could be compared against the theoretical force profile generated in Motion. They were remarkably similar and using Motion eliminated numerous iterations of prototype designs.
We have used this process in other drug delivery device projects too. It was used to calculate force profiles required from springs and other components to drive a complex auto-injector trainer. It’s not just useful in small mechanisms – we have used it extensively in security products such as security gates, to optimise motor, mechanism and component sizing etc.
SolidWorks Motion and Simulation are incredibly versatile tools which are especially useful in optimising designs to suit power and space constraints, particularly for complex mechanisms. We’ve used it many times now and we’re very pleased with how close physical results have been to theoretical models. Simply put, using Motion effectively, especially alongside some physical test data, will significantly reduce development time.
Understand more about SolidWorks Motion here…