The Bioprinter Manufacturer’s Guide to Linear Motion - Part 2

Part 2: Rigidity, Speed & Precision

(Read Part 1 here)

Rigidity

The performance of a bioprinter’s linear motion system rests, literally and figuratively, on its base.?

Wherever high performance is required, sufficient rigidity or stiffness demands close attention to factors such as thickness, frame construction, and materials. All must be consistent with the final performance specifications you want to achieve.?

Rigidity affects factors such as flatness and straightness. For example, a manufacturer may attempt to attach a linear motion rail made of stainless steel, of required thickness and suitably rigid design, to an aluminum plate that’s thinner than the rail. The inevitable result: deflection. (Linear motion components are typically designed to resist forces along the X, Y, and Z axes to prevent this.) Here, the deflection would mean that the rail could curve, however slightly, in the direction dictated by any force applied. This affects smooth travel and repeatability, which in turn can degrade the uniformity of the printed product.?

But even the most advanced linear motion products can’t deliver superior speed or precision if they rest on a base that allows extraneous movement. Traditionally, most 3D printers have been mounted on structures such as sheet metal cabinets or aluminum tables. Unfortunately, these bases won’t deliver the acceptable rigidity demanded by modern bioprinter manufacturing equipment. So instead, the recommendation is for strongly built steel or iron structures or granite bases.?

Another innovative choice is a substructure composed of minerals and epoxy resins. These mineral cast bases furnish printer beds with excellent vibration dampening, strong chemical resistance, and excellent thermal stability. In addition, they can be formed to accommodate any contours and dimensions a given printer requires, including custom-shaped openings, spaces, and wiring channels. They also offer clear technological, economic, and ecological advantages over steel, gray iron, or cast iron.?

Discuss expected loads and printer configuration with the linear motion supplier early so that the resulting system is designed from the start to withstand all the forces and conditions and meet all the accuracy and precision requirements of its intended application.

Speed

The travel speed of a linear motion system essentially defines the printer’s production speed.?

Relatively slow speeds are required for some tasks on some bioprinters to prevent such issues as deformation. On others, excessive travel acceleration can create problems from ringing to ghosting to lack of layer adhesion to filament blobbing. In most cases, manufacturers ask linear motion suppliers to deliver maximum speed wherever possible.?

When the highest productivity or output is required, it’s essential that a linear motion element can accelerate as rapidly as possible. But settle time is often another key metric: how long it takes the rail or other component attached to the moving part (print or beam head, material bed, etc.) to come to rest without appreciable vibration after each acceleration step.?

However, such factors greatly depend upon the printer design, the material, shape, thickness, resolution, and other characteristics of the specific item that the printer is producing; and which linear motion components have been employed.?

Generally speaking, in an optimum configuration, some of today’s high-performance linear motion systems can attain constant velocities with step-and-settle intervals — even at exact positions — of as low as 50 milliseconds. That would allow extremely rapid travel to support the fastest industrial printers available today, which operate at up to 1000 millimeters a second. A discussion between the manufacturer and supplier is required to determine what can be achieved in any specific application.

Precision

The choice of linear motion equipment directly impacts the degree of positional accuracy and repeatability — the precision — that an operating bioprinter demands. Therefore, the linear motion technology employed will impact critical performance requirements for the end application, including accuracy, repeatability, and resolution.?

If the end-user in a bioprinting process employs after-print finishing steps to attain given tolerances or flatness/smoothness specifications, extreme precision in primary printing may not be necessary. However, a good linear motion system for this range of printers might deliver positional precision down to plus or minus 50 or 100 microns.?

However, internal features of the finished item may not be easily accessible after completion. Additionally, bioindustry-leading OEMs are evolving their approaches to minimize extra finishing. Thus, an extremely accurate linear motion may be required to achieve precise dimensions and shapes at every point.?

Many bioprinter applications are now exceeding the level of linear motion equipment precision traditionally required by high-performance machine tools. And as biomanufacturing technologies continue to evolve, expect many applications to demand even higher degrees of precision — such as leading linear motion suppliers design into ultra-precise nanoscale equipment for semiconductor manufacturing. For bioprinter requirements that fall into these latter groups, a linear technology supplier must be willing and able to consult on specific requirements and compare the exact capabilities of possible linear motion solutions to enable a manufacturer to achieve such a whole new level of precision.?

Much depends on the specific printer design and on the item that must be bio-printed. Beyond, a linear tech supplier must address issues from the linear motion system’s stiffness, flatness, load/preload, and construction materials to its operating temperatures and vibration/resonance potential, as well as considering factors such as constant velocity and stroke length. But under the right conditions, a superior linear motion system today can enable certain bioprinters to attain repeatable accuracy from 0.5 down to 0.1 microns

Moving into the Future of?Bioprinter Manufacturing

Today’s advanced linear motion systems can, and are, delivering the precision that bioprinting applications can demand.?

As bioprinter manufacturing continues its explosive development, speeds will increase, efficiencies will grow, and the use of biomaterials will proliferate.?

There is ample room for bioprinters’ linear motion capabilities to grow. For instance, precisely controlling the movement of dispensing elements on smaller and smaller scales can empower bioprinters to manufacture ever-finer somatic structures. Vein tissue was first successfully printed in 2016. Fully functional 3D-printed human organs are predicted in the not-so-distant future.?

The result:?an increasing number of bioprinter OEMs are exploring the benefits of advanced linear motion solutions for their challenging, cutting-edge, and in many cases, unique products. The right supplier can overcome concerns and obstacles to help deliver advantages such as expert design, acceptable lead times, reduced cost of ownership, reliable quality, and rewarding partnership. In addition, the right linear technology can provide critical characteristics such as rigidity, speed, accuracy, precision, miniaturization, customization, material compatibility, and biosafety that enable truly high-performance bioprinting.?

This article is Part 2 of 2 parts.

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The Bioprinter Manufacturer's Guide to Linear Motion Technology