It is a viberatory motor.
These are made in all sizes, some that would shake your entire house, down to the one pictured which is the smallest I have seen.
They have many uses.
Properly sized and mounted to the bottom of a metal tray, they are used to "convey" or move material along the tray.
Attached to screened trays, the will take a material )such as gravel) and classify or size the material through the screens.
This one may have been used as an ultrasonic generator.
There are Viberatory Drives available that will vary the intensity of the unit some. You plug the cord into the drive in that case.
Otherwise, take a look at the picture and imagine the unit setting on its feet with the linear moter to your left.
You will see two sets of vertical springs. The value of those springs, combined with the load, adjusted with the nut & set screw on the rear of the linear motor tune the unit.
By the way, these aren't cheap!
Have fun!!
