"swing" motor electronics

I have a 100v/12volt RV Fridge with a Fujisawa swing (linear) motor. The "swing" motor features a linear moving armature connected directly to the compressor piston (only one moving part). The tag on the unit says 60hz, 20v and 40watts. There seems to be a fair amount of electronics with it including a fair sized transformer. Apparently the swing motor has to work on AC since it relies on reversing polarities to move the armature/piston up and down. How do we get from a 12v DC input to the stated AC requirement. Is this just a hidden inverter. If so how is it any different than running an AC unit from an external inverter. One thing we know is that the swing motor requires a much lower start up current than a conventional motor/compressor. (My 70 watt AC Mini Fridge requires a 1000 watt inverter to get it started).

The trick in the design of the swing motor is matching the input AC frequency to the resonant frequency of the spring loaded armature thus providing the amplitude that would otherwise not be achievable. Is it just a coincidence that this resonant frequency turns out to be the standard 60hz?

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swing motor requires a much lower start up current than a conventional motor

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Hello. Could you please describe in more details what is a "swing" motor, as well as specify what is meant by "a conventional" motor.

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Originally Posted by Yuri B.

Hello. Could you please describe in more details what is a "swing" motor, as well as specify what is meant by "a conventional" motor.

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Probably this:
http://www.sawafuji.co.jp/english/tech/shindou.html