Ours is like this, but about 20 years old. Although it doesn't look much different.
I think the top roller is mounted to a cradle that rides on a single large air cylinder in the center, which allows it to pivot on the shaft of the cylinder. The oscillation amount varies, depending on the belt. There's an adjustment for the oscillation, to make sure the belt travels towards the eye (sensor). The adjustment controls the speed of the oscillation. There's really no circuit involved. Adjust the belt so it moves towards the eye. When it breaks the eye, the eye triggers the cylinder which reverses the travel direction. When it clears the eye, the cylinder reverses and the belt starts going the other way again. I'll have to take another look to make sure that's right, as it seems like there's more travel than my description would allow.
The feedbelt is a large 3 phase motor with a 90° gearbox. Belt speed has a manual control, which I believe changes the width of a V belt pulley. The feedbelt is mounted to 4 acme screws which are motorized to raise or lower the table. There's also a hand wheel to raise and lower for finer adjustment.