Company

  • Founded in 1997 and headquartered in Ann Arbor, MI
  • High-end exercise equipment focusing on physiotherapy and cardiac & stroke rehabilitation
  • Range of products based on their original recumbent cross-trainer model
  • 100,000+ products sold internationally

Challenge

  • Improve "usability" of cross trainer machine by making key component easier to actuate whilst retaining strength under load

Solution

  • Optimize with Tosca Structure for target metrics such as center of gravity, mass, and stiffness
  • Composite optimization results into a new design
  • Verify new design in Abaqus Unified FEA

Results

  • Achieved "usability" criterion (reduced rotational inertia)
  • Reduced stress under load
  • Reduced part weight
  • Numerous parametric design trials compressed into one optimization study

Better Performance with Less Material: Designing with Tosca Optimization

NuStep sought to redesign a key component of their cross trainer to better meet consumer needs. Caelynx helped them achieve the desired results using the latest in simulation software and methodology – optimization – which produced a more focused redesign in fewer iterations than the client had anticipated, saving both time and money.

Double Duty: Easy to Use, Hard to Break

A high-end physical therapy and rehabilitation equipment manufacturer tasked Caelynx with solving a straight-forward problem: the machine was too difficult to operate. More specifically, the machine was meant to act as both stepper and leg press station, and the high inherent resistance of the mechanism impeded this intended multifunctionality. On review, it was found that the overly high resistance was related to the level of rotational inertia in the sickles. These sickles are key components of the machine that must serve a dual purpose: firstly, to oscillate when in stepper mode and, secondly, to bear the force of a 1,000 lb isometric stretch in leg press mode. Therefore, the design criteria were twofold – significantly reduced rotational inertia, but with the ability to withstand the 1,000 lb leg press.
Our products are designed and built around advanced technologies, creative design solutions, and rigorous physical testing. Therefore, the utilization of predictive simulation and advanced optimization is integral to our product development cycle. Our longstanding relationship with Caelynx has helped us generate a number of solutions for truly world class component design.
Roger Fettes, Manufacturing Engineer
NuStep - Ann Arbor, MI
NuStep Tosca topology optimization case study cover What does the optimization process look like and what does it achieve?
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DLC: Case Study: NuStep Direct

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12
%
Reduction in Part Mass
17
%
Reduction in Rotational Inertia
500
lb
Loading with NO Permanent Set
7000
lb
Loading with NO Catastrophic Failure

Working Smarter with SIMULIA (Abaqus and Tosca) Optimization

Discovering New Methods

Rotational inertia is ‘the force required for a desired angular acceleration about a fixed axis’.  Therefore, it follows that there are two methods by which to reduce this force­ – either reduce the mass of the part, or pull the existing mass toward the center of rotation.  Of course, our customer knew this and planned to commission a parametric study in which varying designs would be evaluated with FEA, hoping to reach an acceptable solution.

Using traditional development processes, this would be considered the ‘state of the art’ methodology for solving this type of problem.  However, with the advent of modern optimizations tools – SIMULIA Tosca Structure, in this case – Caelynx was able to design a study that cut weeks and potentially thousands of dollars from the overall cost of the project.

The optimization process

With optimization, one can start with a blank slate and direct the computer to cyclically, incrementally iterate toward a desired result.  In other words, while the traditional approach would have an engineer design a part based on its predicted simulation performance, the optimization approach would automatically redesign – and refine – based on observed simulation performance in a repeating cycle.

The key to optimization lies in correctly expressing – in engineering and FEA terms – one’s intentions to the optimization software.  In this case, Caelynx gave Tosca Structure several constraints (such as design space, draft angle, and wall thickness) and several objectives (such as lower center of gravity, reduced mass, and increased stiffness). With a single FE model solving these numerous objectives, it was simple to get Tosca Structure to reveal effective strategies for reaching the redesign’s various goals.

From those optimization results, a composite redesign was generated – a novel helical structure highly tuned to the load case that the component was intended to endure.  Following successful physical testing, NuStep uses this new design in the T5XR cross trainer.

Results Summary

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