A coupling mechanism includes a pivot assembly and a lifting assembly. The pivot assembly includes a first bracket, a pivot pin, a second bracket, and a cam piece. The second bracket is rotatably mounted to the first bracket via the pivot pin and has a valley portion recessed from one surface thereof. The cam piece is mounted to the pivot pin for holding the second bracket at any angle. The cam piece has a peak portion formed on one surface thereof and received in the valley portion of the second bracket at a closed position. The lifting assembly is adjustably assembled to the second bracket such that the lifting assembly is pivotally assembled with the first bracket.