Machine Design

Feels good, works well:

Custom leadscrew makes for a relaxing massage

Dry water massage machines from Aqua Massage International, Groton, Conn., have a 36-jet assembly which moves back and forth along a linear shaft from Kerk Motion Products. The shaft is a nonball leadscrew made from 303 stainless steel. The leadscrew nut is a nonhygroscopic material with a thermal coefficient of expansion equaling that of stainless to prevent binding.

The makers of the Aqua Massage machines found in shopping malls needed a way of guiding and translating the machine's water-jet assembly back and forth smoothly along a linear shaft.

The assembly could have only a minimum of radial play, vibration, and backlash between the screw and nut. This tight fit ensured customers would perceive the massage action as smooth. In addition, the assembly had to be durable while operating at elevated temperatures. It also had to traverse the 7-ft span of the massager.

In response, Kerk Motion Products Inc., Hollis, N.H., produced a nonball leadscrew and nut assembly with a length-to-diameter ratio of thread engagement of about 7:1, twice that of standard nuts.

It was tough to maintain a constant thread fit on these devices. So Kerk used a special material with a thermal expansion coefficient roughly equivalent to that of stainless steel. This prevents binding while the machine operates. The nut material is also nonhygroscopic.

Kerk Motion Products Inc.,

Embedded PLCs cost less, say European users
A recent survey of purchasers and specifiers of industrial automation components revealed over three-quarters of respondents were aware of products offered with embedded PLCs. The report, from the market research firm IMS Research in Wellingborough, U.K., also states that over two-thirds of respondents either purchase some embedded PLC products or plan to do so within the next three years.

More than 95% of respondents think embedded PLCs cost less than separate PLCs and cost less to install. Profibus-DP, Ethernet TCP/IP, and CANopen were the communication protocols most widely used by respondents having hardware with embedded PLCs. Nearly 90% said communication with other embedded PLCs and program backup facility to a PC were important. Nearly 80% thought remote monitoring form a separate PLC was important.

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