Linkage mechanism for three-section sofa bed

A linkage mechanism for a three-section sofa bed, comprising:

• a first link assembly, comprising a first side pivoted to a front sofa cushion and a second side pivoted to a fixed base frame of a sofa frame, wherein the first link assembly is provided with a locking hole;
• and the front sofa cushion is folded and stored inside the sofa frame or unfolded at a side of a middle sofa cushion through a linkage rotation of the first link assembly;
• a second link assembly, comprising a first end pivoted to the middle sofa cushion and a second end pivoted to a middle segment of the first link assembly, wherein the first link assembly drives the second link assembly to rotate, wherein the middle sofa cushion is allowed to be folded and stored inside the sofa frame or unfolded at a side of a rear sofa cushion;
• a third link assembly, comprising a first side pivoted to the rear sofa cushion and a second side pivoted to a pivot position of the first link assembly pivoted to the fixed base frame, wherein the first link assembly drives the third link assembly to rotate, wherein the rear sofa cushion is allowed to rise and fall;
• and
• a locking assembly, located at a side of the first link assembly adjacent to the front sofa cushion and comprising a locking rod, wherein the locking rod corresponds to the locking hole;
• and when the front sofa cushion is unfolded at the side of the middle sofa cushion through the linkage rotation of the first link assembly, an insertion end of the locking rod of the locking assembly is inserted into the locking hole to prevent the first link assembly from rotating again.