Relax, Reflect, Revitalize, Renew flashes on the website homepage of Aqua Massage International (AMI). Based in Groton, CT, AMI is one of the world's largest manufacturers of hydrotherapy "dry water" massage machines. Its flagship product -- the Aqua Massage Machine -- typically found in the center alleys of shopping malls, is similar in appearance to an MRI machine, and has been described as a cross between a tanning bed and a car wash. Kerk Motion Products helped the company come up with a linear motion solution that could operate reliably under some unusual design constraints.

Increasingly, consumers are turning to alternative therapies like massage to release tension, soothe aching muscles, and relieve pain. Dry water massage therapy is attractive to a broad consumer market: aqua massage therapy yields results in only 10-15 minutes; clients can stay fully clothed during the massage; no physical contact is necessary; and an adjustable touchpad control provides the client with the ability to adjust massage strength and location.

The Challenge: Smooth, Quiet, Long-Lasting Linear Motion

With customer demand at an all-time high, AMI sought to optimize the quality of its machine's design. Specifically, the company needed a linear motion solution capable of guiding and translating the machine's spray water jet assembly, which moves back and forth along a linear shaft. The machine's 36 water jets travel along the shaft, massaging either the full length of the body or a concentrated area, depending on customer preference.

The Aqua Massage machine presented an unusual design challenge. Not only did the linear motion assembly have to be accurate and durable enough to meet demanding speed requirements, it also had to meet the performance specifications while operating at an elevated temperature and over a distance of 7 ft.

"Speed is a crucial factor since the pulsating water jets must be able to quickly adjust from 2 to 10 cycles per second without interruption," said Gerardo Aristi, AMI vice president of operations. "We needed a linear solution with minimum radial play, vibration, and backlash between the screw and nut to ensure a tight fit, and thus a smooth experience for the customer." AMI turned to Kerk Motion Products, one of the world's largest exclusive manufacturers of non-ball lead screws and a vendor with whom AMI had a previous relationship. The challenge presented to Kerk was to produce a lead screw and nut assembly that could satisfy all these requirements.

"The Aqua Massage application posed many obstacles," said Bob Hawkins, an applications engineer at Kerk. "The length-to-diameter ratio of thread engagement required for AMI's machines is about 7:1, twice that of standard nuts. This presented a challenge in maintaining a constant thread fit. The challenge was amplified by the saturated environment in which the nut would operate."

A Custom Solution for Demanding Requirements

After a thorough application analysis, Kerk recommended a unique nut material capable of meeting all of AMI's requirements. "The thermal expansion coefficient of the nut material had to be roughly equivalent to that of stainless steel to prevent a binding condition while the machine was in operation. In addition, the nut material could not be hygroscopic, meaning a characteristic whereby something tends to absorb water." Kerk quickly came up with a custom solution that relied on a specialized nut, combined with one of the company's proprietary non-ball lead screws, which are manufactured from 303 stainless steel and produced with Kerk's exclusive precision rolling process.

A Cost-Effective Solution, a Smoother Customer Experience

AMI was particularly impressed by the cost effectiveness of the solution, and the high level of engineering expertise provided by Kerk, compared to other vendors. "Kerk is able to approach an application from the ground level and provide the highest quality and most cost-effective solution based on its requirements," said Aristi. AMI was also pleased with Kerk's customer service, which has allowed the company to increase its production and meet growing demands.

"Kerk's solution is significantly more reliable and cost-effective than competitive offerings," said Aristi. "Our product delivery is now excellent with quicker than average turn-around on our blanket orders of 200-250 products. It was a challenge that many other companies could not have met."

One could say that Kerk's custom lead screw solution has "revitalized and renewed" AMI's entire product line.