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Moving coil parts rejectors `out-perform pneumatics`

03 December, 2007

A Californian company specialising in moving coil actuators, SMAC, has developed a system for sorting and rejecting parts at high speeds on production lines which, it claims, has numerous advantages over pneumatic cylinders and other technologies presently used for these duties.

According to SMAC, one drawback of pneumatic cylinders is that they contain several static and dynamic seals whose efficiency deteriorates over time. This causes friction and "sticktion", slowing down the pneumatic system, especially when cycle times are varied. The longer a cylinder waits without moving, the higher the static friction breakaway force needed. It is not uncommon for this variation to be up to 50ms.

Pneumatic systems are also dependent on the speed and reaction time of their solenoid valves. DC solenoid valves typically have a variance of ±10ms. With AC valves, this variance can double. The total variation in cycle time can be as much as 50ms.

SMA claims that because the MCA system runs on precision linear guides, the static breakaway forces are only around 1% of those of pneumatic cylinders, resulting in cycle time variations of less than 1ms.

Another limitation of pneumatics, says SMAC, is that seal wear limits their lifetimes. The life of such a cylinder is around 10 million cycles when used in applications where controlled impact and end-of-stroke cushioning are used.

The MCA system will, by contrast, last for around 100 million cycles when used in similar applications. This is because the dampening and cushioning are servo-controlled. The actuator coil provides a programmed reduction in speed. The actuators typically draw less than 2A at 24 or 48V, so heat generation is minimal and has no detrimental effect on cycle life. SMAC asserts that its actuators will last 10–25 times longer than pneumatic cylinders in similar applications.

Two other drawbacks of pneumatic actuators, according to SMAC, are their noise and inefficiency. While some silencing and muffling can be applied, the noise of the cylinder impacting at the end of stroke cannot be silenced.

By comparison, SMAC argues, the moving coil actuators are extremely quiet. No waste energy is exhausted, and the heat generated is just 5–10°C.

A final advantage of MCAs over pneumatics, according to SMAC, is that they are cheaper to buy and operate.




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