Designer's Corner 23349

DN Staff

May 5, 1997

3 Min Read
Designer's Corner

Brushless slip ring

Engineers rely on slip-ring technology to transmit data through rotating interfaces. Conventional slip rings employ fixed brushes that slide across the spinning rotor's surface to pick up signals. Worn brushes require replacement, and the sliding action over the rotor may create unacceptable noise levels that degrade the ability to transmit high-rate data streams.

Slip rings normally employ only two to four points of contact. During rotation, impedance varies as the distance from the ring's lead to the brush contact changes. The brushless slip ring employs a full complement of rolling ball contacts sandwiched between inner and outer conductive rings.

Continuous contact combined with minimal torque, gives more constant impedance/reactance, less noise, and longer life.

Fifth Dimension Inc., 801 New York Avenue, Trenton, NJ 08638, 609-393-8350.

0 Hz - 15 Hz, measured

Crankshaft/camshaft position sensing, wheel- and shaft-speed sensing, and other automotive applications require precise revolution detection.

Variable-reluctance sensors have been used for such duty, but are not accurate at low speed immediately after engine start-up. Also, the signal output of such devices varies relative to speed, demanding threshold adjustment at additional circuit expense. Hall-effect sensors may be employed, but applications are limited to a narrow temperature range.

By directly applying a semiconductor magnetoresistive (SMR) element to a silicon substrate, it is possible to affect a dramatic improvement in precise revolution detection. Made of Indium-Antimony (InSb), such SMR devices transduce magnetic flux changes to resistance changes over a -40C to 150C temperature range. High sensitivity eliminates amplification before conversion to digital signals.

Yasu Ishiai, Panasonic Automotive Industrial Group, 44768 Helm St., Plymouth, MI 48170, Fax: 313-455-9336, or [email protected].

Wireless encoder

To minimize noise, typical encoders employ six signal wires: A, B, and index differential. Adding two more for power and ground raises the number of wires linking motor and controller to eight.

Here's a better method. Transmit encoder signals over an infra-red path. "Phantom" wireless encoders multiplex sensor information into a single signal which is decoded at the stationary amplifier/controller.

Benefits, besides wireless data transmission, include low noise, high reliability, less maintenance. Applications? Linear motors, multi-axis systems.

MFM Technology, Inc., 200 13th Ave., Ronkonkoma, NY 11779, 516-467-5151.

Dispense valve controls surge

Used to dispense greases and silicones employed in assembly processes, the Model 735HPA dispense valve features an internal adjustment mechanism to control the opening surge common among high-pressure dispensing devices. Surge results when pressurized material is suddenly expelled at the start of the dispense cycle. To prevent surge, the user removes the hose from the quick-connect fitting at the top of the valve, then uses an Allen wrench to turn the stroke limit stop. This action changes piston stroke, and thus limits spool movement. By adjusting spool movement, the user can regulate both the amount of opening surge and end-of-cycle snuffback, for better control without drooling.

Robert Tourigny, EFD Inc., 977 Waterman Avenue, East Providence, RI 02914-1378, 401-434-1680.

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