Reinventing Machine Design Part 3: Doing It Right

By Tom Kevan

Fig 1: This photorealistic rendering of the ATLUM-2 was generated by ProENGINEER Wildfire 3.0. It shows the rotating lathe, laser interferometer used for position feedback, and cutting knife (in blue). All photos courtesy of Boston Engineering Corp.

Some members of the engineering community will tell you that mechatronics methodology is simply sound design practice, that forward-thinking engineers have been using this approach for a long time. That’s true. But the methodology is far from being the standard operating procedure of machine and device designers.

  To find true mechatronic practitioners, you must identify engineers and firms that follow an interdisciplinary, system-level approach to design problems and integrate new collaboration, communication, modeling, and simulation tools into their design processes. This is where you’ll find mechatronics success stories; and where you’ll find a competitive edge.

The Challenge
One such success story is a project to develop instrumentation required for the neuroscientific study of brain function undertaken by Boston Engineering Corporation (BEC). A local academic institution retained BEC because researchers wanted to build an accurate 3D model, or working electrical diagram, of sub-cellular neuron interconnections. This requires slicing thousands of cross-sections of brain tissue, scanning each with an electron microscope, and then combining the images to create a complete picture.

  To slice cross-sections with thicknesses on the order of 10 to 20 nanometers, researchers needed an ultra-microtome, an electromechanical instrument with a very sharp blade (see Figure 1). The ultra-microtome uses a repetitive slice-and-advance motion, where the tissue sample passes over the blade.

  While several companies sell off-the-shelf ultra-microtomes that typically are called upon to slice a few samples at a time, BEC needed to create one that would run automatically to avoid tying up highly trained lab technicians for long periods of time. The new ultra-microtome would have to deliver thousands of cross-sections while running for days or weeks. Each sample is photographed by a scanning electron microscope at various levels of magnification to produce a repository of images. The hope is to use pattern-recognition software to map the brain within the next three to five years.

Starting Point
A scientist at the research institution, not an engineer,  took the design process of a prototype as far as he could. BEC started its job of perfecting the initial design using two methodologies. These included the mechatronics methodology and the phase-gate development process.

  Mechatronics requires the synergistic integration of the mechanical, electronics, and controls disciplines throughout the design process. “We used the mechatronics approach because a system like this is so complex and so interdependent on the different disciplines that there’s no way to just have a serial methodology,” says Matthew Reck, program manager at BEC. “We always have all three of our disciplines represented in status meetings,  design reviews, and brainstorming sessions.”

  The phase-gate development process is a formalized way of structuring development into a series of stages. “We follow four phases,” says Reck. “Phase One involves specification development, where we interview our clients and learn about the existing technology … and the specification requirements of the machine.

“In Phase Two, we come up with concepts for all facets of the machine—mechanical, electrical, and control. Mechanically, we come up with multiple CAD models. Electrically, we develop schematics and control models. We do a lot of simulation and a fair amount of early architecting in our control system.

“We come up with state diagrams and early theory of operation of the machine,” says Reck. “Once we have agreed on a concept with our client, we hold a preliminary design review. With the approval of the concept, we move to phase 3, which is detailed design, where the concepts take on more tangible form…. At the end of phase 3, we do a critical design review with the client…. Then in phase 4, we fabricate, build, and test the design that we created in the previous steps.”
The System

  The ultra-microtome developed by BEC, called the Automated Tape Collecting Ultra-Microtome Rev. 2 (ATLUM-2), is a blend of mechanical,  electrical, and control components. On the mechanical side, the instrument incorporates air bearings, laser interferometers, and the latest servo motion controls. The control side consists of a sophisticated host system that BEC developed using National Instruments’ LabVIEW.

  The host control application runs on a Windows PC and communicates with two major subsystems. The first subsystem handles motion control, and it uses Aerotech’s A3200 modular network motion control system. Communications within the subsystem rely on a FireWire network, so there is very little cabling.

  The second subsystem performs data acquisition and control,  using National Instruments’ PXI data acquisition and control platform. This tier collects data from sensors that monitor cutting force and temperature. The subsystem also controls simple serial devices that perform functions like turning on power supplies and executing level control.

  Both subsystems feed data back to the host PC, where the lab user interfaces with the machine. The ATLUM-2 can operate on both manual and automatic cycles.

  The instrument handles system faults, tracks data, and logs errors and inputs. Theoretically, it can run up to two weeks unattended,  collecting samples and notifying designated personnel through alarms and messages if there is a problem.

Tools of the Trade
Mechatronics requires greatly enhanced collaboration and communications. And with the various engineering disciplines working closely together, the need to find ways to cultivate common visions of design project requirements and engineering concepts is critical. To accomplish these goals,  BEC availed itself to many traditional and cutting-edge tools.

  BEC’s mechanical engineers used PTC’S Pro/ENGINEER and SolidWorks to depict mechanical models that were key in both internal development and communicating with the client. The electrical and control engineers on the design team modeled with PTC’S MathCad and MathWorks’  Simulink. And its software engineers used the LabVIEW visual programming environment. BEC supplemented these core software packages with Microsoft Visio, a diagramming software package, and Atlassian’s JIRA, a browser-based task-tracking and project-management solution.

An Enabling Design
In this design and development project, the ROI is really measured in the advancement of the academic institution’s research. The ATLUM-2 is an enabling tool that promises to take science to the next level in understanding how the brain functions.

More Info
Atlassian Pty Ltd.
San Francisco, CA

Boston Engineering Corp.
Waltham, MA

Dassault Systèmes,SolidWorks Corp.
Concord, MA

FreeMind

Marquette University
Milwaukee, WI

The MathWorks Inc.
Natick, MA

Microsoft Corp.
Redmond, WA

National Instruments
Austin, TX

Parametric Technology Corp. (PTC)
Needham, MA

Tom Kevan is a New Hampshire-based freelance writer specializing in technology. Send your comments about this article to [email protected].