Application Digest

Know when to select a servo system

Ed Steiner, President, Industrial Indexing Systems

Accurate, efficient production machines often require flexible motion control systems to meet performance goals. Choices include a simple variable-speed drive, low-cost stepper motors, or a full closed-loop servo system.

A servo system is the best choice if the motion trajectory exhibits any of these characteristics:

Smooth, slow-speed movement.

  • Precise speed control, less than 1% ripple.

  • High repetition of start-stop motions.

  • Full torque at zero speed.

Certain load characteristics indicate need for a servo system:

  • Changing inertia or friction loads.

  • Unpredictable load changes.

  • Need to reverse direction without delay.

In addition to these guidelines, servo systems are especially suitable for specific control requirements. For example, those applications where the controller must know when load stalls, or moves outside the desired trajectory, benefit from a closed-loop servo system. So do situations calling for multi-axis control with closely coordinated motion or anti-collision requirements.

Engineers should also examine how the load interacts with the servo system. Finally, supplier selection is as improtant as the system itself. Choose a vendor with demonstrated experience--one that wants to be a partner, not just a supplier.

To speak with an applications engineer from Industrial Indexing Systems, call (716) 924-9181 or FAX (716) 924-2169.

Improve gasket design with wise material choice

Geoff King, Product Manager, Norton Performance Plastics Corp.

Today's engineers are no longer confined to EPDM, neoprene, and butyl when choosing materials for electronic enclosure gaskets.

One material to consider: foam. It uses less material than a solid, weighs less, and handles better during installation. It also remains more supple over time and recovers better after compression.

Three foamed polymers or elastomers are another attractive option for electronic enclosures: PVC, thermoplastic rubber, and rubber-modified polyester.

It also makes a difference to the enclosure design engineer how the foam was produced. Cast-and-slit foam sealants are made like a big roll of carpet, then slit into widths or die cut to order. Thus, the top and bottom surfaces are smooth, but sides expose cut cells.

Extruded dry foam adds some design benefits to a gasket. Custom cross sections are possible, which can lead to more effective and economical designs. And, the entire exterior has a continuous skin.

When a permanent seal is required, butyl-coated PVC foam is an excellent choice. The joint has all the advantages of butyl: tenacious adhesion, low moisture and vapor transmission, and excellent aging properties. Yet, the core has all the desirable qualities of a flexible closed-cell foam.

Within the last few years, a new breed of foam-in-place gasketing has captured a lot of attention. Called Dynafoam(R), it goes on and sets up as readily as a thermoplastic. The material is a one-part, moisture-curing, rubber-modified polyester. Gaskets as large as 0.75 inch in cross-section have been produced in a single pass.

To speak with a Norton applications engineer, call (518) 642-2200.

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