Pardon me, Prof, I've been quite unclear.

Perpetual in a sense that a device will keep on moving with a constant force (40kgs minimum-meaning, excess force), without the aid of fossil fuel, water, wind, magnets, solar, battery, coal, nuclear, etc... or something more powerful enough to power up a normal household consuming 15-20 kw a day.

I am not sure if anything of such kind have already been invented, most probably not yet. Otherwise, market would have already been flooded with it.

So, what I would really wanted to ask (especially to those who have a broad background in physics), is it possible to create such a device by using gravity alone??? Or, such a device will always end up in equilibrium?

Well, gravity is always available, unlike air, water, and solar... and fossil fuels are already 'endangered species',uh, i mean, almost running out.

And... just, if ever, such a device exists... does it break the Law of Conservation of Energy?