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Solenoids > Application Examples: Solenoids Used in Data Storage Cassettes
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| Solenoids Used in Data Storage Cassettes |
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Mass storage of computer data has long been a costly function. Many methods have been developed over the years to provide the huge storage capacity often needed for large databases. These have included large computer room disk drives and magnetic tape on reels. The reel methods prove valuable for system backup but the mega hard disks provide the fast access time needed for everyday system operation. While both systems function nicely in large mainframe applications, their cost and bulkiness have discouraged wide use on individual PC's or networks. As PC's became more powerful, alternate mass storage methods were developed to fill the niche. One approach utilized 8mm cartridges similar to VCR cassettes. To provide the desired capacity, several cartridges are stored in a rack. A single tape reading head is then fed the appropriate cartridge via a two-axis robotic system. The desk top size device must be automatic, compact and low cost. This dictates low cost actuators and controls, a natural for solenoids. One key function is the actual capture and ejection of the cassettes. The forces and displacement for direct actuation were rather large. Space simply would not permit a large solenoid.
In order to keep cost, mass, power drain, and physical size to a minimum, one manufacturer decided to use a Z-axis motor to not only extend and retract the cartridge but also to capture and eject it. A set of spring-loaded fingers on the Z-axis carriage provides the capture phase. Triggering the tape ejection requires a slight reversal of the motor so that a trigger arm can be actuated. To prevent the solenoid force from being large, a solenoid is mounted perpendicular to the carriage motion. Thus, when actuated, the tip provides a stop to trigger the arm as the carriage backs gently into contact with the actuated plunger shaft. An internal spring retracts the shaft to allow carriage passage during the actual transport sequence. A modified .50 x .50 inch tubular solenoid is adequate for this momentary function. By enlarging the external end of the push shaft, earlier bending problems have now been eliminated. Small size and mass make for a compact, quick responding robotic subsystem. Low power consumption, simplicity, and competitive device cost have allowed this manufacturer to meet the required price targets.
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