Linear Shaft Servo Motor Can Replace Traditional Ball Screw

I'd Like to tell you about a customer who is an OEM manufacturer of high-performance filtration systems for medical, energy, and industrial businesses. As part of their system, they must continually verify the integrity of their filters by moving a proprietary sensor beneath the filter medium to test minute amounts of particulate matter inside a contained system. It is very important that the test system itself does not contribute any contamination.

After discussing a traditional linear motion system with a recirculating ball screw, there were some definite problems identified, including wear and outgassing, high noise, friction, and heat. Also, a motor would have to be coupled to the screw through the contained system’s wall. We then weighed the advantages of using a linear shaft servo solution from Nippon Pulse America. Typically, a ball screw or belt drive mechanism could be used, but we determined that for this application, the linear shaft servo was appropriate.

Linear Shaft Motor System Configuration | Cross Company

Figure 1: Nippon Pulse Linear Shaft Servo Motor System Components

The Linear Shaft Motor (LSM) is a very simple design consisting of a coil assembly, called the forcer, that encircles a patented round magnetic shaft. This design has many advantages when compared to traditional linear motion ball screw and less accurate belt drive systems including:

  • It’s more compact and lighter in weight than traditional ball screw assemblies and doesn’t require a traditional rotary motor inside the containment chamber or coupled through the wall.
  • There are no belts and pulleys creating mechanical inaccuracies and releasing contaminants as they wear.
  • The extreme smoothness that is inherent in the LSM is a result of no cogging in the coreless, ironless design. This results in smoother more repeatable test results.
  • The LSM is quiet with a noise level that is practically non-existent, and many times less than that of other mechanical systems - especially a ball screw with recirculating bearings. This is important for any laboratory or medical applications of this filter system.
  • The (non-critical) air gap of .5 to 5 mm allows easy alignment and creates non-contact movement, eliminating any friction and wear that would cause the release of materials that could contaminate the test field.
  • The high efficiency of the LSM uses less energy (up to half as much). This, along with the elimination of friction, results in less heat generated.
  • The LSM eliminates the mechanical losses incurred in a traditional ball screw or lead screw, as well as the outgassing of materials due to wear and friction. This results in better accuracy and repeatability, especially over long time operation.
  • Because it is a linear servo motor, you get all the advantages of high speed, acceleration, accuracy, and repeatability of linear servo technology in a much smaller and lighter weight package than traditional iron-core linear motors.

The modular construction of the system (shown in the attached diagram) will allow this customer to “build in” the solution into the base of his stainless steel structure as an integral part of the filter system. Cross Company can supply the Linear Shaft Motor, shaft supports, rail and bearing block support, and a linear scale encoder, plus the servo drive and electronics for the entire test system.

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Steve has been with Cross Company's Motion Solutions Group for 27 years. He's worked on projects from the design & testing of the Space Shuttle at NASA to getting peanut butter in the middle of a chocolate cup and everything imaginable in between!

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