Hybrid Tattoo Machine Inks In Sanitation
Coreless DC motors yield hybrid tattoo machine with improved hygiene, flexibility, and performance.
Tattooing today is a multimillion dollar industry, fueled as much by crowded conventions as hip tattoo studios. Forget about the image of a grizzled sailor sporting a bicep tattoo of a heart emblazoned with the word "Mom." Body art today has grown sophisticated and nuanced, with artists rendering everything from tribal tattoos to fantasy landscapes formed of multiple layers of color and painterly effects. And yet, even as the industry breaks new ground, many of the tools in use are based on old design. Neuma Tattoo Machines set out to change that, developing an autoclavable electromechanical tattoo machine that weighs about 30% as much as a conventional tattoo gun. Fueled by small, robust coreless DC motors from MICROMO, the low-noise, low-vibration system has blazed the trail in terms of precision, ease-of-use, and hygiene
For more than a century, the two-coil electrical tattoo gun has been the de facto standard in the industry, prized by artists for its direct vertical motion and the amount of variation it offers in needle pressure. The design is electric, though, which makes the guns impossible to truly sterilize. The bang-bang motion creates both noise and vibration. Coupled with weights of typically 8 to 10 oz, coil guns also present repetitive-strain issues for tattoo artists, who may work six or eight hours straight on a single design.
The pneumatic tattoo machine provides an alternative, with a 1.8-oz handpiece that can be tossed into an autoclave when the client gets up from the table. Because needle motion is driven by a rotating cam, however, pneumatic machines drive the needle with little or no variation in pressure. In addition, the rotary cam imparts a 50-50 duty cycle to needle motion, keeping needle in the skin longer, which can impact healing. “It's more of a rigid design whereas the older technology is more of a cushioning design," says Carson Hill, master tattoo artist and founder of Neuma. "Most artists like the cushioning design because it's easier to get the tattoos to heal properly.” Perhaps more important from a practical standpoint, a pneumatic machine requires a bulky, power-hungry air compressor. That might be fine for a business operating out of a studio but for artists who do the bulk of their work at conventions, lugging around a 50-lb. compressor is simply not feasible.
When Neuma set out to reimagine the tattoo machine, their goal was to design a system to bring the best of both worlds. They wanted to keep the ease of use and hygienic advantages of the pneumatic design while providing enhanced portability and reliability, and more variability in needle motion and force. The result was the Neuma Hybrid, a lightweight, autoclavable tattoo machine that offers options while providing the kind of cushioned, variable-needle performance that tattoo artists need.
Modular Design
For the Neuma Hybrid design, the team wanted a modular machine that could easily switch between pneumatic and electrical power so that an artist could run the machine in pneumatic mode while in the studio but while on travel they could switch to an electrical drive module that runs off wallplug power.
The question was how to interface electrical drive module with the handpiece. The most obvious method was mechanical gearing, but the only way to ensure a sterile system would be if the electrical module could be sterilized along with the handpiece. Although autoclavable motors are available, they added significant weight and cost to the design. Neuma needed a noncontact alternative.
The answer proved to be a magnetically coupled design. The bottom of the handpiece features an impeller fitted with strong magnets (see figure 2). They line up with six corresponding magnets embedded in a disk attached to the shaft of the motor in the electrical module (see figure 3). When the motor/magnet-disk assembly turns, it applies force to the corresponding magnet disk on the impeller. That, in turn, rotates the camshaft, which moves the needle. Because electrical module is driven by the DC motor, it provides significantly more flexibility than pneumatic version, allowing artists to adjust motor speed and, hence, needle speed. Perhaps best of all, once an artist finishes a tattoo, they can remove and reliably, efficiently sterilize the handpiece.
Although the design seems straightforward, the demands it placed on the motors were nontrivial. Because of the long hours involved in tattooing, careful ergonomic design was essential to minimize fatigue and risk of repetitive-strain injury in users. The motors had to be both light and compact, as well as robust enough to survive high duty cycles.
After considering suppliers, the team chose coreless DC motors from MICROMO, driven by an 18 V power supply fitted with a rheostat. "They're consistent and high-quality motors that will last and not be as erratic," says Hill. "For us it was a tradeoff of quality versus price and we felt like it was a good balance.”
The application requires a surprising amount of torque. The magnetically coupled design means that the motor does not simply turn the camshaft. It has to supply enough muscle to rotate the mass of the magnet disk and pull along the handpiece impeller, which in turn works against the inertia of the camshaft and the needle assembly.
Finding the right motor was an iterative process. In an attempt to satisfy size and weight constraints, the group chose the smallest motor that could provide the necessary torque. That wasn't the only trade-off involved, however. In the rotating-cam design, the faster the motor turns, the faster the needle moves, which affects not just the speed of the tattooing process but the quality of the art. Although the first motor generated enough torque to turn the impeller, it simply did provide sufficient rpms to do the job. “We started out with a smaller motor that had a similar amount of torque but a lower high-end speed, which was a problem,” says Hill. “We ended up learning that we wanted more speed than we realized.”
With the new motor, the machine could reach the speeds desired by customers, but just barely. When the engineering team took a closer look at the system, though, they realized that the problem wasn’t the motor at all but mechanical issues that contributed to load. “In the beginning, it seemed like the motors weren't fast enough or strong enough," says Hill. "A lot of people were running these motors at the full 18 V to get the speeds they wanted. What we learned was that there were a lot of little bugs in the system that we had to work out like friction, critical dimension, thermal management, and materials. By ironing out these other details and making the motor’s job easier to do, we found they really are more than fast enough.”
The group also optimized the cam design to alter needle motion. Instead of the 50-50 duty cycle, the needle now only spends about 40% of the time in the skin. With some rotory machines, tattooists can only make a single pass on skin without beginning to cause damage. The modified cam of the Neuma Hybrid lets the artist make multiple passes on the same area, which allows them to create more painterly effects.
In addition to the reduced duty cycle, the hybrid machine integrates a cushioning system that provides performance very close to that of coil-based machines . “It's not a rigid hit," says Hill. "You get the best of both worlds, the cushioning effect that’s desirable from the older technology and the reliability and maintenance-freecharacteristics of the new technology. Plus, it’s cleaner.”
The Neuma Hybrid has won multiple awards for design excellence, including the 2009 Good Design award from the Japan Industrial Design Promotion Organization and the 2009 Spark! Award. Its hygenic advantages, enhanced by an antimicrobial finish on the casing, have attracted the attention of the U.S. Occupational Health and Safety Administration, which is considering their design as a gold standard for future tattoo regulations.
As far as Neuma goes, they couldn't be happier with the system—and with the motors. "We've had zero issues," says Parker Forbes, the Neuma technician who builds most of their production units. "In fact if there's ever a repair, it’s never an issue with the motor. We've been building with them for probably a year or so now so we’re definitely happy with them.”