Nut material provides extras for massage machine

Edited by the Engineeringtalk editorial team Feb 24, 2006

Linear motion product guides and translates massage machine's spray water jet assembly, which moves back and forth along a linear shaft.

Aqua Massage based in Groton, Connecticut, USA, is one of the world's largest manufacturers of hydrotherapy dry-water massage machines.

Typically found in shopping centres, these capsule-like machines look like MRI machines, and have been described as a cross between a tanning bed and a car wash.

When the company was founded in 1990, its machines were intended for fitness and sports centres, spas, and clinical and chiropractic settings.

Increasingly, consumers are turning to alternative therapies such as massage to release tension, soothe aching muscles and relieve pain.

Consumers have already poured more than $3.5 billion into massage services and products and some experts estimate that demand for these products and services will top $1 trillion by 2010.

While traditional massage is popular among consumers of all ages, and attracts a particularly upscale, affluent clientele, dry water massage therapy is attractive to a broad consumer market, including people that would not otherwise consider a traditional massage.

As opposed to traditional massage therapy, which can take one hour or more, aqua massage therapy yields results in 10 to 15 minutes.

Additionally, aqua massage clients can stay fully clothed during the massage; no physical contact is necessary to complete the session, and an adjustable touch-pad control provides the client with the ability to adjust massage strength and location.

Aqua Massage wanted to improve the quality of its machine's design.

Specifically, the company needed a linear motion product 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.

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 more than 2m.

"Speed is a crucial factor since the pulsating water jets must be able to adjust quickly from two to 10 cycles per second without interruption," said Gerardo Aristi, Vice President of Operations at Aqua Massage.

"We needed a linear product 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".

Kerk Motion Products was asked to produce a lead screw and nut assembly that could satisfy these requirements.

"The Aqua Massage application posed many obstacles," said Bob Hawkins, Applications Engineer at Kerk.

"The length-to-diameter ratio of thread engagement required for the 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".

After a thorough application analysis, Kerk recommended a nut material capable of meeting all the 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, a characteristic whereby something tends to absorb water.

Kerk came up with a custom design that relied on a specialised nut, combined with one of the company's non-ball lead screws, which are made from 303 stainless steel and produced with a precision rolling process.

Aristi said: "Our product delivery is now excellent with quicker than average turn-around on our blanket orders of 200 to 250 products".

"It was a challenge that many other companies could not have met".