Power transmission apparatus having two belts

A power transmission apparatus, comprising:

• a driving joint unit having a first driving gear fixed to a first driving shaft and a second driving gear fixed to a second driving shaft and disposed on a straight line together with the first driving shaft;
• an operating joint unit fixed on an operating shaft and having an operating gear rotating together with the operating shaft;
• a first operating belt connected to the first driving gear and the operating gear to apply a torque to the first driving gear and the operating gear in the same direction;
• a second operating belt connected to the second driving gear and the operating gear to apply a torque to the second driving gear and the operating gear in opposite directions;
• a driving link having one end connected to the first driving shaft or the second driving shaft to be freely rotatable thereon and the other end connected to the operating shaft to be freely rotatable thereon;
• and
• an operating link fixed to the operating shaft.