RSS Feeds
Designers' corner
By John Lewis, Technical Editor -- Design News, September 20, 1999
Expanding rail plug
Mounting linear guide rails from below is the best way to prevent corrosion from coolant, but it isn't always practical. Often counter bored holes are used to bolt rails down from the top. To seal such holes from coolant most manufacturers sell plastic or brass plugs, others offer stainless steel cover strips that snap on top of the rail. While cover strips are a quicker solution than installing plugs, coolant can still leak under the strips and eventually cause corrosion.
Chamfering the bolt hole edges may ease plug installation, but chamfers create troughs that can retain machining debris which ultimately decreases carriage wiper life. Although installation can be a little more tedious, rail holes without chamfers ensure a tight plug fit with no trough for contaminants to collect. A two piece stainless steel plug outperforms plastic or brass plugs in open-chip areas to guarantee leak-proof sealing of the screw-head space.
With this mechanism a thin stainless steel cylinder with two annular rings slips into each hole and rests on the bolt. A tapered plug is then pressed into the ring, causing it to expand and contact the edge of the hole. Once installed, the plug sits perfectly flush with the top of the rail providing a tight seal and a smooth surface for the carriage wiper.
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| The seal ring fits loosely into the counterbore. A tapered plug expands the ring when inserted. The plug mounts flush with the rail to provide a tight seal, and provides a smooth running surface for optimum wiper function and life. |
John Skaltsas, Schneeberger Inc., 11 DeAngelo Dr., Bedford, MA 01730; Tel: (781) 271-0140.
Grid encoder
The PP 201R exposed incremental two-coordinate measuring system determines object position with measuring steps to 10 nm in the plane. A grid plate and scanning head work to eliminate positioning errors due to orthogonality errors in the stage.
Square elevations are applied to a glass substrate at 45 degrees to the measuring direction. Non-contact scanning is based on the interferential measuring principle. Each scanning head provides two 90 degree phase-shifted sinusoidal output signals with a signal period of 4 micrometers and provides a 68- 3 68-mm measuring range with outside dimensions of 98 3 98 mm.
| With the scanning unit mounted directly under the workpiece rather than on the edge of the stage, orthogonality errors in the stage do not result in positioning errors. |
John Thormodsgard, Heidenhain Corp., 333 East State Pkwy., Schaumburg, IL 60173; (847) 490-1191.
Wirebond safety notch
When subjected to a damaging current surge at the device's output, triacs and solid state relays (SSRs) incorporating triacs generally fail in the shorted or "on" mode. To prevent this from happening in SSRs, users typically incorporate an external or separate triac fuse to protect the SSR's load and output. This separate-fuse solution, though, consumes valuable board space and can add substantial cost to the end design.
A new wirebond technology alleviates the need for separate parts by notching the wirebond connected to the internal die-form triac. When a damaging over current is present at the triac it generates heat at the stress notch causing it to fail at the wirebond rather than inside the triac.
With this technology, the triac (or SSR output) fails open or "safe," eliminating, in many applications, the need for an external fuse or protection circuitry.
| Over current generates heat that is focused on the stress notch, causing it to fail at the wirebond rather than inside the triac. |
Christina Lewis, Omron Electronics, Inc., One East Commerce Dr., Schaumburg, IL 60173; (847) 843-7900, ext. 257.
Disposable deformer
Even the best designs need overload protection. Emergency overrunning end-stops on machine tools and impact protection on vehicles are examples. Unlike conventional damping systems such as friction springs or hydraulic buffers, DEFORM plus, as an overload protection system, transforms the kinetic energy of impact into deformation work to protect equipment. While not reusable after permanent deformation has occurred, it offers the following benefits:
Lower cost
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Smaller installation space
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Lower weight, the elements being manufactured from special high-density polymer
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Easy replacement of used elements
Eight sizes from 42 to 510 kN (10,000 to 115,000 lbf) are available. Comprised of synthetic material, shock-absorbing elements withstand temperatures between -25 and +50C (-13 to +122F.)
Small impacts and static loads are absorbed without plastic deformation. But to ensure integrity, once deformation is visible, the element must be replaced. New elements are easy to stock, and used elements can be returned to the supplier for recycling.
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| Recyclable elements deform permanently when subject to a high shock load that might otherwise damage machinery. |
Lisa Karlich, Ringfeeder Corp., Box 691Westwood, NJ 07675; (201) 666-3320.
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