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| Solenoids in Parcel Sorters |
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Large parcel sorters are used for heavy boxes and packages. To divert these materials, rubber cleats (shoes) are mounted between the rollers on chain-driven conveyors. These cleats are guided by a railway beneath the conveyor. At switch points, the cleats can be diverted to follow an intersection track. This causes them to slide across the full width of the conveyor thus forming a row of moving bumpers which redirects the parcel to merge with another conveyor line.
Previously, the switch points were actuated by air cylinders. The use of air made installation costs very high. Normally, one construction trade union was needed for the pneumatic installations and a second for the electrical controls. Also, the response time of the air system used was not rapid enough to allow the manufacturer to meet their product improvement goal of doubling the speed of operation. The manufacturer set their desired specification as a maximum transfer time of 10 milliseconds.
Even for solenoids, 10 milliseconds is difficult. Rotary actuation was chosen due to the simplicity, compactness, and ruggedness offered compared to linear actuators requiring linkages. As the design evolved, two things became evident. Every time the spring was increased for faster speed of return, the solenoid had to become bigger to produce enough torque to power back. Also, along with this size, came an ever increasing power requirement. Only one product choice would work - a bidirectional Ultimagā solenoid.
The Ultimag approach allowed identical speeds in both directions. To achieve 10 milliseconds still required a high peak energy, capacitive discharge circuit. The addition of a very light biasing spring was required to keep the unpowered solenoids in predetermined positions. Extended life and low friction operation were also important considerations.
The Ultimag and associated electronics became the right answer for this difficult task. Bi-directional solenoid operation has opened new opportunities vs. stepping motors and other technologies in high speed, limited rotation applications.
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